Just saw this thread and want to draw your attention to some microscopic differences between two MBA 15"s I purchased in the last few months:
https://forums.macrumors.com/threads/mba-15in-trackpad-speed-at-max.2396904/post-32369703
In summary, I bought two midnight color 15" MBAs, and the trackpad on the first one feels coarser and more sticky, with higher stiction and a sluggish feel that makes it unpleasant to use. The second one feels normal and like any other MacBook. The surface coating looks different, so this may be something they fixed in later batches. The keyboards don't feel the same either, the older one is lighter, the newer one is heavy and tiring to use. Can't win.
I'm curious, if you have or don't have this issue, what color you have, and what the manufacture date is. To find out, open Terminal, type "ls -l /", and look for the "cores" row.
Midnight, Mar 17: sticky feeling
Midnight, May 5: normal and smooth