I have created a BSP house in one map. i have grouped the few hundred bsp’s and then copy/paste group into differant map. After it ate up my 32gig of ram it crashed so i put in an SSD as a dedicated pagefile which stopped the crashing but takes about 4 or 5 hours to paste using all the ram and constant pagefile in use.
Today it took over 3 hours to paste and used over 137 gig (32 ram, rest in pagefile on ssd).
If i export as a mesh its a quick process but meshes do not give the same lighting effects as bsp’s and are not useable until i have time to learn more. I have a deadline looming this week.
This is in version 4.8.3