How big is the SkUp file once the DWG is imported? Window>Model Info>Statistics to find out how many lines and faces you’re dealing with. Post a screen shot of that to get feedback on how big is big. The cache of sorts is purging everything unused so that it is really removed from the file. And layering so you can control visibility and give OpenGL a fighting chance to keep up. Some more good general advice below.
I have had big DWGs clog up sketchup before, had an arena model that pretty much broke it, 300+ mb. I ended up cutting the model into quarters and working on 4 separate files. There have been a few moments when copying everything and pasting into a new window has seemed to yield some improvement but I can’t justify why that worked, could have been a one time corrupted file.