I commissioned this awesome script from Felix "Xilefian" Jones and he allowed me to post it here.
This Plugin optimises the way spritesets are handled by Scene_Map by caching them. By using a cache, the memory usage and CPU usage is reduced massively.
You can even choose after which number of map transitions it cleans the cache. In my eyes its a must have problem for big projects with many parallax maps.
This also fixes completly the bug that the game starts to get slow when spamming the menu.