Recently I had to experience that the viewport will be extremely slow when I create a larger building. Layout was almost useless but fortunately I found a small solution how to speed up.
One thing to switch of the lights and turn shading to No light mode. It will be faster five times. The disadvantage is that all texture will be darker (please, let me know why If anyone knows). The another solution is to use dynamic display object’s bounding box for Display mode/ Shaded/ Objects/ dynamic display usage .