Upload & Sell: Off
First, let Lr generate all of the image previews before you start browsing - even if it means letting it run overnight. You might need to select all images and then tell Lr to rebuild the previews or else it might stop at the current folder.
Second, if you used the standard size previews in step 1 and are trying to zoom in to 100% (1:1) then Lr will regenerate full size previews on the fly. This will be slow and will gobble up drive space. The solutions are to restrict your 1:1 Library module browsing, go back to the first step and use 1:1, or better yet use the Develop module.
1:1 browsing is often faster in the Develop module than in the Library module if the 1:1 previews do not already exist, and you have better control over editing once you are there. Otherwise, develop is slower than Library because Develop always reloads the file data and builds a new preview.