Hello,
Indeed, the MPXA6115A is designed to operate from 15 to 115 kPa.
The accuracy of the MPXA6115A should meet the requirements of the specification described in the data sheet.
Unfortunately, Freescale does not have characterized the data specs out of the calibrated range.
In case it is useful for you, I recommend to refer to the Figure 5.Output vs. absolute pressure from the datasheet:

I hope this material will be useful for you.
If I misunderstood your question, feel free to let me know. I will be glad to help.
Have a great day.
David Diaz.