In general, the games in renpy that I played. Almost no developer makes a cache system load in advance images, videos, screens or whatever is necessary, thus avoiding spikes in the memory/processing of the computer that can lead to crashes in weaker systems.
anyway if that's the case, not much, you can do unless if you improve your computer
I'll give you an example of my game; one of the options is the fetishes tab which is very heavy loaded with information. the fps meter when you open it drops from 60 to 3 ~ 0 with the cache system loading-it with my fps stays at 60 ~ 58
It's only an example, not necessarily the truth as I said can be many things.