Should I use materialised view?

Question

I am using the following sql in my code. This takes a long time to execute and I need to tune this. Please review and suggest if I should be using a materialized view instead.
Main Select statement for interest calculation
SELECT          intratechgcur.SECURITY, intratechgcur.srl_no, intratechgcur.schg_type,
     CASE WHEN intratechgcur.effective_date < ADt_Start_Date THEN ADt_Start_Date
                         ELSE intratechgcur.effective_date END AS start_date,
     CASE WHEN intratechgcur.effective_date < ADt_End_Date
                         AND NVL(intratechgnext.effective_date, ADt_End_Date) > ADt_End_Date THEN ADt_End_Date
                         ELSE NVL(intratechgnext.effective_date, ADt_End_Date) END AS end_date,
                    intratechgcur.rate, intratechgcur.face_value, intratechgcur.listing_int, intratechgcur.comm_prod_int,
                    intratechgcur.sec_create_int, intratechgcur.int_type, intratechgcur.interest_key, intratechgcur.margin,
                    intratechgcur.FLOOR, intratechgcur.cap, intratechgcur.reset_freq, intratechgcur.cmpd_y_n, intratechgcur.cmpd_freq,
                    intratechgcur.comp_type, intratechgcur.int_day, intratechgcur.int_day_1, intratechgcur.int_day_2, intratechgcur.int_dtls_yn
FROM               v_intratechg intratechgcur, v_intratechg intratechgnext
WHERE               intratechgcur.SECURITY          = AS_Security
AND          intratechgcur.effective_date < ADt_End_Date
AND               intratechgnext.SECURITY          (+)= intratechgcur.SECURITY
AND               intratechgnext.srl_no          (+)= intratechgcur.srl_no + 1
ORDER BY      intratechgcur.SECURITY, intratechgcur.effective_date, intratechgcur.srl_no ;
The code for the view V_intratechg is;
CREATE OR REPLACE VIEW V_INTRATECHG AS
SELECT     security,
     schg_type,
     effective_date,
     SUM(1) over (PARTITION BY security ORDER BY security, effective_date ASC, schg_type ASC) AS srl_no,
     face_value,
     rate,
     listing_int,
     comm_prod_int,
     sec_create_int,
     int_type,
     interest_key,
     margin,
     FLOOR,
     cap,
     NVL(reset_freq, 'DAILY') AS reset_freq,
     NVL(cmpd_y_n, 'N') AS cmpd_y_n,
     NVL(cmpd_freq, 'DAILY') AS cmpd_freq,
     NVL(comp_type, 'N') AS comp_type,
     int_day, int_day_1, int_day_2, int_dtls_yn
FROM
     (SELECT     security.security, 'IM' AS schg_type,
          GREATEST(security.prv_int_dt, NVL(security.allot_date, security.prv_int_dt),
          NVL(security.first_int_date,security.prv_int_dt)) AS effective_date,
          DECODE(intday.int_day_1, 'ACD', NVL((SELECT interest_amt FROM securityschddtls A WHERE security.security = A.security
          AND A.adhoc_schd_date > GREATEST(security.prv_int_dt, NVL(security.allot_date, security.prv_int_dt),
          NVL(security.first_int_date,security.prv_int_dt))
          AND a.rectype ='L' AND A.ADHOC_SCHD_DATE = (SELECT MIN(ADHOC_SCHD_DATE) FROM securityschddtls
WHERE      securityschddtls.adhoc_schd_date > GREATEST(security.prv_int_dt, NVL(security.allot_date, security.prv_int_dt), NVL(security.first_int_date,security.prv_int_dt))
     AND securityschddtls.security = A.security AND securityschddtls.rectype='L')),
          NVL(secchg.rate, security.interest)), NVL(secchg.rate, security.interest)) AS rate,
          NVL(secchg.face_value, security.face_value) AS face_value,
          NVL(secchg.listing_int, security.listing_int) AS listing_int,
          NVL(secchg.comm_prod_int, security.comm_prod_int) AS comm_prod_int,
          NVL(secchg.sec_create_int,security.sec_create_int) AS sec_create_int,
          NVL(secchg.int_type, security.int_type) AS int_type,
          NVL(secchg.interest_key, security.interest_key) AS interest_key,
          NVL(secchg.margin, security.margin) AS margin,
          NVL(secchg.FLOOR, security.FLOOR) AS FLOOR,
          NVL(secchg.cap, security.cap) AS cap,
          NVL(secchg.reset_freq, security.reset_freq) AS reset_freq,
          NVL(secchg.cmpd_y_n, security.cmpd_y_n) AS cmpd_y_n,
          NVL(secchg.cmpd_freq, security.cmpd_freq) AS cmpd_freq,
          NVL(secchg.comp_type, security.comp_type) AS comp_type,
          NVL(secchg.int_day, security.int_day) AS int_day, intday.int_day_1,
          intday.int_day_2, 'Y' AS int_dtls_yn
          FROM          security, assetype, intday, securityschddtls secdtls,
                    (SELECT     secchg.security AS security, secchg.call_date AS effective_date,
                    NVL(secchg.rate,0) AS rate, secchg.face_value,
                    SUM(1) over (PARTITION BY secchg.security ORDER BY secchg.security,
                    secchg.call_date ASC) AS srl_no,
                    NVL(secchg.listing_int,0) AS listing_int, NVL(secchg.comm_prod_int,0) AS comm_prod_int,
                    NVL(secchg.sec_create_int,0) AS sec_create_int,
                    secchg.int_type, secchg.interest_key,
                    nvl(secchg.margin,0) as margin, nvl(secchg.FLOOR,0) as floor,
                    nvl(secchg.cap,0) as cap, secchg.reset_freq,
                    secchg.cmpd_y_n, secchg.cmpd_freq, secchg.comp_type, secchg.int_day FROM          secchg) secchg
          WHERE          security.asset_type     = assetype.asset_type
               AND          security.int_day          = intday.int_day
               AND          assetype.int_y_n           = 'Y'
               AND          security.rectype          = 'L'
               AND          assetype.rectype          = 'L'
               AND          intday.rectype               = 'L'
               AND          secchg.security (+)= security.security
                    AND          secchg.srl_no (+)= 1
                    AND          secdtls.security (+)= security.security
                    AND          secdtls.srl_no (+)= 1
                    AND          secdtls.rectype (+)= 'L'
          UNION ALL
          SELECT     schedules.security,
               DECODE(schedules.schd_past_yn, 'Y', 'RP', 'RS') AS schg_type,
               DECODE(intday.int_day_1, 'ACD',security_cashflow.start_date,security_cashflow.inflow_date) AS effective_date,
               --commented by vijai
               -- DECODE(intday.int_day_1, 'ACD', intschdamt.amount, NVL(intratechg.rate,security.interest)) AS rate,
               DECODE(intday.int_day_1, 'ACD', intschdamt.amount,decode(security_cashflow.start_Date,intratechg.value_Date, intratechg.rate, security.interest)) as rate,
               decode(nvl(schedules.tot_face_value - schedules.cum_face_value,security.face_value),0,security.face_value,schedules.tot_face_value - schedules.cum_face_value,security.face_value) AS face_value,
               NVL(intratechg.listing_int,security.listing_int) as listing_int,
               NVL(intratechg.comm_prod_int,security.comm_prod_int) as comm_prod_int,
               NVL(intratechg.sec_create_int,security.sec_create_int),
               NVL(intratechg.int_type,security.int_type) as int_type,
               nvl(intratechg.interest_key,security.interest_key) as interest_key,
               nvl(intratechg.margin,security.margin) as margin,
               nvl(intratechg.FLOOR,security.floor) as floor,
               nvl(intratechg.cap,security.cap) as cap,
               nvl(intratechg.reset_freq,security.reset_freq) as reset_freq,
               nvl(intratechg.cmpd_y_n,security.cmpd_y_n) as cmpd_y_n,
               nvl(intratechg.cmpd_freq,security.cmpd_freq) as cmpd_freq,
               nvl(intratechg.comp_type,security.comp_type),
               nvl(intratechg.int_day,security.int_day),
               intday.int_day_1, intday.int_day_2,
               DECODE(intratechg.security, NULL, 'N', 'Y') AS int_dtls_yn
          FROM     v_schedules schedules, security, intday, intratechg, v_schedules intschdamt, security_cashflow
          WHERE     schedules.security          = security.security
          AND          schedules.red_yn      = 'Y'
          AND          security.int_day               = intday.int_day
          AND          security.rectype               = 'L'
          AND          intday.rectype                    = 'L'
          AND          intratechg.security (+)= schedules.security
          AND          intratechg.value_date(+)= schedules.schd_date
          AND          intratechg.rectype     (+)= 'L'
          AND          intschdamt.security (+)= schedules.security
          AND          intschdamt.schd_date (+)= schedules.schd_date
          AND          intschdamt.red_yn (+)= 'N'
          AND           security_cashflow.inflow_type      = 'INT'
          AND           security_cashflow.inflow_date     = schedules.schd_date
          AND           security.security               = security_cashflow.security
          AND           schedules.security          = security_cashflow.security
          UNION ALL
          SELECT     intratechg.security, 'IR' AS schg_type,
               intratechg.value_date AS effective_date,
               NVL(intratechg.rate,security.interest),
               security.face_value,
               NVL(intratechg.listing_int,security.listing_int),
               NVL(intratechg.comm_prod_int,security.comm_prod_int),
               NVL(intratechg.sec_create_int,security.sec_create_int),
               nvl(intratechg.int_type,security.int_type),
               nvl(intratechg.interest_key,security.interest_key),
               nvl(intratechg.margin,security.margin),
               nvl(intratechg.FLOOR,security.floor),
               nvl(intratechg.cap,security.cap),
               nvl(intratechg.reset_freq,security.reset_freq),
               nvl(intratechg.cmpd_y_n,security.cmpd_y_n),
               nvl(intratechg.cmpd_freq,security.cmpd_freq),
               nvl(intratechg.comp_type,security.comp_type),
               nvl(intratechg.int_day,security.int_day),
               intday.int_day_1, intday.int_day_2, 'Y' AS int_dtls_yn
          FROM     intratechg, security, intday
          WHERE     intratechg.security          = security.security
          AND     security.int_day               = intday.int_day
          AND     intratechg.rectype          = 'L'
          AND     security.rectype               = 'L'
          AND     intday.rectype                    = 'L'
          AND     NOT EXISTS     (SELECT     1 FROM          v_schedules schedules
                         WHERE          schedules.security     = intratechg.security
                         AND          schedules.schd_date     = intratechg.value_date
                         AND          schedules.red_yn          = 'Y'))
          ORDER BY security, srl_no
The code for the view V_schedules is;
CREATE OR REPLACE VIEW V_SCHEDULES AS
SELECT schdall.security,
          schdall.schd_date,
          schdall.schd_type,
          schdall.percent,
          schdall.units_o,
          schdall.units_n,
          schdall.amount,
          schdall.sequences,
schdall.act_sch_dt,
     schdall.security_n,
          schdall.prior_act,
     schdall.red_amount,
          schdall.ben_refer,
     schdall.round_method,
schdall.round_dec,
schdall.average_y_n,
     schdall.schd_past_yn,
     CASE WHEN schd_type IN(sysschd.red, sysschd.disred) THEN 'Y' ELSE 'N' END AS red_yn,
     SUM( CASE WHEN schd_type IN(sysschd.red, sysschd.disred) THEN schdall.red_amount ELSE 0 END)
                              over(PARTITION BY schdall.security) AS tot_face_value,
SUM( CASE WHEN schd_type IN(sysschd.red, sysschd.disred) THEN schdall.red_amount ELSE 0 END)
                              over(PARTITION BY schdall.security
                                   ORDER BY schdall.security, schdall.schd_date ASC) AS cum_face_value,
     SUM( CASE WHEN schd_type IN(sysschd.red, sysschd.disred) THEN schdall.red_amount ELSE 0 END)
                                   over(PARTITION BY schdall.security
                                   ORDER BY schdall.security, schdall.schd_date DESC) AS to_be_redeemed ,
          SUM(CASE WHEN schd_type =sysschd.INT THEN 0 ELSE 1 END)
                                   over(PARTITION BY schdall.security,schdall.schd_date,schd_type)
                         AS no_of_schd
FROM
               (SELECT      schedules.security_o AS security,
                              schedules.schd_date,
                              schedules.schd_type,
                              schedules.percent,
                              schedules.units_o,
                              schedules.units_n,
                              schedules.amount,
                              schedules.sequences,
                              schedules.act_sch_dt,
                              schedules.security_n,
                              schedules.prior_act,
                              schedules.red_amount,
                              schedules.ben_refer,
                              schedules.round_method,
                              schedules.round_dec,
                              schedules.average_y_n,
                              DECODE(schedules.schd_type,'RED','Y','Y') AS schd_past_yn
          FROM           schdpast schedules
          WHERE           prior_act = 'A'
          AND                rectype = 'L'
          UNION ALL
          SELECT           schedules.security_o AS security,
                              schedules.schd_date,
                              schedules.schd_type,
                              schedules.percent,
                         schedules.units_o,
               schedules.units_n,
                         schedules.amount,
                    schedules.sequences,
                    schedules.act_sch_dt,
               schedules.security_n,
               schedules.prior_act,
                    schedules.red_amount,
                    schedules.ben_refer,
               schedules.round_method,
               schedules.round_dec,
               schedules.average_y_n,
                    'N' AS schd_past_yn
          FROM           schedules
          WHERE           prior_act = 'A'
          AND                rectype = 'L'
          AND                Process_date IS NULL ) schdall,
          (SELECT           MAX(redschdtype) AS red,
                         MAX(disredtype) AS disred,
                              MAX(intschdtype) AS      INT
                              FROM sysparamschd
          WHERE rectype = 'L') sysschd
ORDER BY security, schd_date, schd_type

Answer 1

Too much SQL... makes me eyes hurt.
I think you're running down the wrong alley here. The very first and fundamental principle of performance tuning is identifying the performance problem. Saying that there is a problem is not identifying the actual problem.
You cannot run down the alley with a knife looking for a performance problem to kill if you do not know how it looks like. Good that you are running though - the old Klingon saying of "a running warrior can slit more throats" hold very true. :-)
Why is the existing SQL slow? You first need to identify that. Sure, a materialised view can make the end-query much faster as it has no longer to do all the work - that has now been done in batch by a DBMS_REFRESH job updating and maintaining that materialised view. But that work is still done... so have you actually fixed the cause of the performance problem, or merely hid it by addressing the symptoms?
How does one find and identify the underlaying performance problem with too-much-SQL-that-makes-Billy's-eyes-hurt? Software Engineering 101. Take any complex problem. Break it down into lots of smaller little problems. Solve each on in turn.
Take the SQL, break it down into simpler pieces and check each for performance issues. Look at the execution plan and cost. Determime if you (via the physical db design) are providing optimal I/O paths to the CBO in order for it to get to the required data with as little I/O as possible.
Once you deal with the facts, you can make an informed decision or whether or not a materialised view will actually fix the cause of the performance problem.