i did often read about slow preview times with many sprites but thought it cant be so worse..
now i got to a point where its just ridiculous, in a project with 600 24*24 Sprites (one sprite object, so would be one spritesheet) and 200 16*16 (another spritesheet, so we would have two now), a total size of 50kB, its faster to export the game, find a failure, fix the the failure, export again and run the game compared to just previewing it, the preview is at that time at ~50% loading.