This is pretty normal. Lightroom is very sluggish adjusting the previews when you sync a large number of images. It's always been that way and you often have to move through to see the previews update. This is even true on the very fastest machines.
When I've worked in smaller batches it works no problem (20-50 photos).
Using Lightroom Version 5.71
Working on a DELL PC Intel I7 3.40GHz processor, Windows 8, 64-bit OS, 24 Gib of RAM
That is not too exciting to hear. I would love to do more Timelapses but that part of the process sucks, It's such a great feature but bogs down the process, especially if I miss a few random frames and have to redo the rendering.
Adobe is there a FIX???