They should be compatible if they are clean (without any mods - default files). I can't tell what state your scripts were in when you created the game save in 1.2.15. It all depends on what state the scripts were in and what changes were made to the scripts by the developers after the game save was created. If a game save doesn't work then you try another. The game save is screwed up when the scripts do not match the data (scripts) in the saved game save.Will my saves from v1.2.15 be fully compatible with this version or should I start a new game?