you might want to reduce the exp needed to level a skill or revamp the system entirely, after doing the 30+ encounters 3 times to level each of the players stats,
and the over 40 times to level the sisters cardio the game gets major slow down even freezing at times.
I don't know if this is a slight optimization issue or if ren'py isn't made to do the same thing 100's of times to grind stats.
This is probably due to the fact that the browser export from renpy is in the beta stage, still many bugs to sort out. What you just mentioned is not an issue in the download version. Also the reason the XP needed rises so fast is due to the fact that there's nothing after that point in the game so it acts as a deterrent of sorts. After I add more content I'll lower the XP requirements.