The more objects in the room, the more GPU is needed; same with the number of NPCs present. The CPU usage is not an issue as even a C2Duo can run it without problems.
Concerning RAM, the actual version of the game uses about 2 GB. Only users with a 4 GB smartph... PC using integrated graphics solutions might have problems with this (2GB game + 2 GB shared RAM (actual textures take 2 GB VRAM) + system resources 300 MB to 1 GB). But let's be fair... those PCs are not meant for gaming, but for office purposses.
I also realized load times over HDD (7200 rpm SATA III) are pretty high (game start takes over 12 sec to get main menu operational, NPCs spawn delay 3 to 5 secs when changing locations), so installing the game in an SSD is highly recommended.
A Ren'py is really not the solution (and I seriously doubt it would even happen); but perhaps providing a low-res texture pack, reducing the props to a half in locations (also provided in a separate pack for low-end PC users), limiting the ammount of NPCs present (PC included) to 5, and using simplified hair models (might look like a plastic cap, but will surely improve performance), in addition of using classic map graphics, and reducing PP and Shadow quality, should do the trick.