Marc welcome to the forum. I understand making the jump from Adobe to ON1. It seems a little strange at first, but after a while, you don't really notice it. I will admit there are some things that you will miss from lightroom. I personally miss using multiple radial adjustments at the same time. Now I have to create multiple local adjustments with the same settings. Minor setback, but a setback nonetheless. I hope you enjoy using the software. Good Luck!

I noticed that you are using the "Accurate" Raw Preview mode. If the files are too large, or there are a lot of them, then it may slow down the preview. Try switching this to "Fast" and then that should help out. By doing this, you are telling ON1 to use the Low Res JEPG embed with the RAW file for your preview. This is usually less sharp and the colors are more of an average than a true representation. Nonetheless, this should help to speed up your previews. You may also want to off load your scratch files to an SSD card to improve the speed of your computer if changing the RAW preview mode doesn't help.