Moist heat sterilization

Can we perform post sterilization of product at 115 degree Celsius for 20 minutes.

Depends on the product!

You have to look at two things. 1 - does your product withstand the sterilization process (what Boomer was referring to), and 2 - do you get sufficient kill at 115 for 20 minutes.

For 1 - you should run tests (stability, efficacy, etc.) to see if your product is still viable after a steam sterilization cycle
For 2 - run Fo calculations, and see if you are getting the required reduction in bioburden (do you need a 6 log reduction, 5 log reduction, etc.)
For 2 - You will also have to confirm sufficient bioburden reduction by running Biological Indicators in your process validation studies.

If what Jared recommends doesn’t work (product unstable), you may have to try Tyndallization.