Unreal engine 4 is slow while trying to move pieces only (small building)

I don’t think it’s a bug. I think it’s probably a heavier load for the brushes than it is for a mesh.

I’m guessing Brushes would be a level two where static meshes would be a level one (I don’t know the exact terms on this). I just figure this is the case as I’ve seen in the past with computers.