Is this only happening to you guys in the compact editor, or also in Slate? (according to last post Slate is faster)
You can try going to Render Setup > System > System settings and lowering the quality of the material editor previews, or switching them to the default 3ds Max ones. This will speed up preview rendering.
Also make sure that you are using "High performance" or similar power plan in Windows. I noticed many times that with other plans the 3ds Max UI is sluggish unless you are rendering at the same time (the CPU is not in full throttle mode).