there is a way to replace the proxy geometry by any other object. Every single vertices and faces consume memory of ram, meaning that if you have several proxy in the scene, not only the Sketchup feedback is slower, but you could be wasting memory of ram needed to achieve a high resolution render. That is why it is a good idea to replace the actual low polygon proxy representation for an even more simpler geometry.
On this page of the site you can watch the video online Thea Render --- Proxy Objects --- Tutorial #20 with a duration of hours minute second in good quality, which was uploaded by the user Thea Render Tutorials 14 December 2014, share the link with friends and acquaintances, this video has already been watched 2,472 times on youtube and it was liked by 10 viewers. Enjoy your viewing!