It's not the maps themselves, it's the scripts on them. I managed to reduce the lag of Hikari's tomb for the next update, and I will be working on them as I come across them. To be honest even I don't understand exactly how the game decides how much memory is being used, as the same rules don't seem to apply to every map. I'm experimenting as I go along.
As for a sprinting-lock, I have been considering it for a while now. Might add an option next patch, though it won't be turned on by default.