Keep in mind that, if you double the number of blocks used, the map will take 4 times longer to build. Also, avoid using texture scales of less than 0.25. For faster builds of simple levels, disable light and visibility calculations on the map compiler options. If this doesn't work, use models instead for the small decals (like desks and doors) as they build instantly. You can use blocks for the exterior walls and for walls that block view of other objects.