I have the same issue. In earlier versions it was awesome. Now it is pretty useless to me because (as you say) everytime I move a light, change a value, move geometry, move the sun, pretty much anything I change, max freezes and I have to wait around 10 senconds to get it working again. And this is true for heavy as well as light scenes. With a Brand new scene and a simple model with an override material, whenever I move the sun max freezes. It was awesome till 1.2, from 1.3 on I've been having this issue. I have a 8350, 32gb 2400mhz, ssd, asus crosshair v formula z, gtx 1080, 850w antec, everything watercooled.