For Rent and laggy walls

I think walls are laggy if you edit a rentable section on a lot with that category already. I'm building a lot with a rentable unit now, but as I did not switch lot category yet, it is not laggy at all. If nobody moved in yet in your case, you could try reverting to regular residential cat., but if you already played with tenants I don't know how smart that would be. Also, switching category causes (naturally) problems if you set any lot challenge or rental rules for any unit on the lot.