If you have a slow preview on some scenes? => Be sure to set the render engine to FireFly while building the scene or working in the Material room.
There is a bug in Poser that slows the UI down with SuperFly selected as render engine.
Yeah, it is a strange bug; The selection of the render engine having an influence on the UI speed.
Simply select FireFly for scene building and Material room work, and ONLY select SuperFly when done and ready to render.
Best regards, Tony