Something's definitely going wrong if the game is running with FPS that low. Sadly I don't think I can help with this, since it's made with GM8, a legacy version of Game Maker with no official support anymore.
Since it's my first time ever making an idle game, I never thought about separating tick speed from FPS. But if I ever make another idle game in the future, that's something I'll do for sure. But thanks for the comment and sorry I couldn't be much help.