Photogrammetry from GM certainly affects performance how ever well optimised it is. That’s fine if you are normally running at 50/60 FPS like I do, but useless on my previous marginal system. Also having to many areas of the photogrammetry in a small region can magnify the effect.
E.g. I have photo scenery for Bristol, Bath, Cardiff, Yate & Chipping Sodbury, but I can’t run them all together. Don’t try the Avonmouth one, it will destroy performance on any system unfortunately.
I have a lot of really nice cenery by Mark Taylor and John Lovell. Judging by performance, they have both improved their optimisation as time goes on.