I think there are several factors involved that cause the slowness. I am myself trying to solve these issues for the material panel (not looking at layers panel as others have better knowledge about it) and try to find fixes if possible.
As there are probably several factors causing these issues that means it is harder to figure out fixes. I hope to find them one by one and fix them.
I have had a meeting with @Iyang_Huang and with @Elias_Brulin and both have problems with slow material editor. The cause seems to be different. In Elias case rendering and raytraced work ok, but he does not get rendered thumbnails. And because the thumbnails are not rendered, then they are not cached. Next step is to figure out why the previews are not rendering for Elias.
There is a simple test one can do to check if a thumbnail preview gets rendered or not.
Step1: Open a new empty model.
Step2: Open material editor.
Step3: Create a material of type gem.
Step4: Right click and hold button down and drag mouse to rotate preview.
As one rotates the preview Rhino creates quick previews that has this transparent skin. When one stops the rotation, then the rendered preview is created. This preview is more shiny. If you do not get the more shiny preview, then the rendered previews do not work.
It is also possible to turn off previews by setting these advanced settings to false.
