Hi, unfortunately the port to ren'py is quite in a raw state, I think after some time the creator of the engine will be able to optimize it.
As for dividing the game into parts, it's a very time consuming task, and if you also make different options for the end of the part, it's even harder.
If we take into account the fact that this is our first project of such a mashstab, we simply would not have had the opportunity to realize it 5 years ago (that's how long slutcraft is in development).
Thank you for your open comment, we always enjoy reading your feedback.