1st-gen apple pencil, 2nd-gen 12.9" iPad Pro. Photoshop is absurdly laggy and slow to respond to the pencil. Doesn't happen in Lightroom or any other Adobe programs, nor any non-Adobe programs. (Clip Studio Paint, Procreate, etc.) Even just drawing a plain black line with the most basic hard round brush tool, with pressure options and smoothing turned off, has a delay of approximately half a second between when I make the stroke and when the line appears. Every other tool is the same, as is most navigation. The program responds to my finger presses just fine, but it's awful with the pencil. No other programs running in the background, iPad and pencil are both fully charged, etc.
I have the first-Gen. iPad Pro 12.9", and I see this too. It's especially bad using the healing brush. PS may take 10 seconds or more to finish tracking a small scribble I've made with the brush. By way of comparison, I have a brand new iPad Pro 11" and don't see this at all.
Since we haven't seen many Adobe engineers yet on this new forum, I suggest we report this on the feedback site.