Is it relevant to update my iphone 4s running on ios 5.0.1 to 5.1.1

is it relevant to update my iphone 4s running on ios 5.0.1 to 5.1.1

It's your choice. You may find that some apps might have 5.1 as a minimum requirement, so you won't be able to download/upgrade those apps.
These pages list what were included in the latest updates :
iOS 5.1    : http://support.apple.com/kb/DL1504
iOS 5.1.1 : http://support.apple.com/kb/DL1521
If you update to 5.1.1 then you will get what was included in 5.1 as well

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