Well, I'm not about to defend Adobe, as the performance of LR has not been great. Even with v10.2, on starting the program there's time to learn a new foreign language to fluency while it starts up.
On the new version (10.2) and a PC with AMD 3900X processor, going to a 36Mpixel raw with no preview, going from grid to full view, and then immediately clicking it to zoom in, it's about 4 seconds until the zoomed-in view is fully rendered (and "loading..." disappears). Scrolling through images in grid view is faster... at the moment.
What I've found in the past (pre 10.2) is that it may work fast, and then get into a state where scrolling from one image to the next takes several seconds. Optimising the catalog several times in a row, exiting LR each time, can speed things up. That's with a catalog of just under 80,000 images.