It’s no secret that Lightroom can run a bit sluggish at times, especially when trying to render previews of high-megapixel files from cameras like the Nikon D810, Canon 5DS R, or the Sony A7r II. I hate staring at the dreaded “loading” icon as I move from image to image. Rather than sitting and waiting for each image preview to render individually, here are two options to have Lightroom build the previews in the background. This way, you can get up and get some coffee while the computer does all the work….

Source: Building Standard Previews in Lightroom