Limited sampling rate

Hi,
I've got a VI that reads in analog inputs. The DAQ device I'm using is a PCI 6229. I believe that the max. sampling rate of this device is 250kS/s. So, if I were were to take inputs from 16 channels I thought I could enter a sampling rate of 15kS/s (since 250/16 > 15) . However, when I look at my output data, I can find that the sampling rate was actually 14925 S/s not 15000 S/s which I entered.
When I enter a sampling rate of, say, 14kS/s the data shows that it's actually 14kS/s. So I'm wondering whether the maximum limit of my sampling rate is around 14.9kS/s and not 15kS/s.
Cheers.

It didn't produce any error messages when I ran it with 16 input channels and 15kS/s sampling rate (all my input channels were at RSE). I'm just confused as to why the sampling rate on the output file is shown to be 14.9kS/s. I just ran it with 1 channel and 250kS/s sampling rate and the output file did show that the sampling rate was in fact 250kS/s. I've attached my VI for you to have a look.
Probably different to my original question; I've used an example shipped with NI for some analog output, and I'm not sure what a particular function of it used for. I've attached a picture of it here as well (the part which I don't understand circled). 
Attachments:
multichannel_daq3.vi ‏303 KB
example.PNG ‏6 KB

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