You are trying to go back to the 2015 version, is that right?
If so Please try this:
- uninstall PA from Steam
- unsubscribe from all mods in this game's Steam Workshop
Delete the following folders if still present:
- Steam/SteamApps/common/PA
- C:/users/<UserName>/AppData/Local/Introversion/Prison Architect/
(keep any valued save games, of course)
To see the AppData folder you'll need to enable View Hidden Items in File Explorer.
- opt into the 2015 version
Now install PA again and see how that goes please!