Due to the size of the game, accessing game files through joiplay may cause longer load times, however if you are using a new version of joiplay (1.01.430 iirc) there are widespread complaints about performance on this game, all of which can be resolved by using a previous version of joiplay and the renpy plugin.
Alright, copypaste time.
You can either downgrade to version 1.01.400 and disable auto-update in the playstore
https://www.patreon.com/posts/joiplay-1-01-400-51867946?l=en
Or you can enable beta builds in said playstore and use 1.01.500
Either works
Make sure you have the RenPy plugin too
If you have further problems, try the JoiPlay Discord