What operating system? Exactly what happens when you start to boot up? Error message? Crash?
You can't go back to 2015.2 but you could install CC 2014 which would open up your CC 2015 files:
Waiting for a previous version to install....
Win 10. I click on the icon, and after about five seconds get a dialogue box telling me that Windows can't boot the program and will stop. No crash.
Installed the previous version and she booted fine... But lost all my preferences. Crikey.