Hello, there are two issues here: RenPy is not optimized as an engine, and, as is often the case, the device's specifications are not ideal. I don't know for sure what device you have, but it may need more time to load.
Here are some tips:
+ Free up more space on your device
+ Unload all other applications running in the background from RAM before launching the game
+ Reboot your phone before starting the game