I'm speaking entirely from my own experience with Ren'Py games. I wouldn't be surprised if the upgrade to Python 3 significantly improves performance, but at the end of the day, it is still Python, a rather notoriously slow language.
Honestly, I feel like KiriKiri would be a better choice of engine, especially given its what Fate, HA, and OG Mahoyo used. That being said, it has its own set of problems, including a criminal lack of documentation, and KiriKiri 2 being nearly 20 years old, with krkrz not seeming to be under active development...
I've also been working on my own engine for some time now, though even calling it in its infancy right now is an overstatement... Eventually, once its actually remotely useful, I'd like to do an auto-port from Mahoyo to it as a tech demo. If it can handle everything there, I'll be very happy. I imagine that's still quite a ways away though.