Is there a way to build small previews on import that load really quickly, so I can go through images and rate while import is proceeding? I'm currently building smart previews and as I move image to image, I'll usually get the "loading" label that can last a second or two. I know that sounds short but it seems long when going through the process and I have to either slow down or risk missing an image as I blast past.
To get them to load quickly your standard preview size needs to be large enough to fit on your screen. Check your catalog's settings standard preview size to see if it is bigger than your display size. On some displays like some of the retina or 4K displays you might have to get it to make 1:1 previews. If you are going through these full screen, what is likely happening is that either your previews are too small for your display or you are simply too quick and the previews haven't been generated yet. It's likely the latter if you are reviewing while it is still importing in the background. In this case creating "smart previews" probably is actually hurting you as it takes extra time and cpu to do that making it take even longer before your normal previews are generated.