Ever since “Auto” mode of the environment importance sampling was introduced, any changes to environment map became very slow. So slow that in fact on many occasions dragging a UV transform slider does not appear to have any effect at all as the rendered viewport update rate is slower than the slider refresh. This completely kills interactivity when transforming environment maps for lookdev purposes.
It appears that the entire “heuristic” the auto mode does is that it sets the importance map resolution to the same resolution the environment map is. So even as small HDRI map as just 4x2k has 4k importance map, which is a complete overkill even in a case of a map with a tiny, super bright HDRI sunspot.
Here’s a video:
The issue is all the more frustrating given that Auto mode is the default now, resulting in poor performance out of the box even for relatively low res environment maps.