That's pretty weird, try deleting the game save files, they are located in "C:\Users\[your username]\AppData\Local\TU", maybe the character generation script is failing by generating too many objects, I don't know of such a bug because when I work in the game I work with save data and in my case I have no worse performance after generation, even using data from previous versions, but it could be a bug in some specific customisation parameter 🤔
If you don't mind, please let me know if deleting the save data restores the performance you had before, as I'd be very grateful to find a possible bug. And sorry again, I know that bad performance is something that can really ruin the experience 😞