I used to have the same problem (on Windows only, not Mac) but it seems to have been fixed as of a month or two ago.
There's a noticeable delay when doing operations on Nixpkgs (to the tune of a quarter-second), but that's a huge repository.
Everything else is instant.
I ran into this at first on a large-ish repo. watchman fixed it: https://jj-vcs.github.io/jj/latest/config/#filesystem-monito...
The biggest killer was performance. jj operations took several seconds for me, whereas git is instantaneous no matter how big the project. Maybe this is fixed now.
But also honestly I felt like there was a bit more mental burden to using jj. When I switched back to git, it was like a weight off my shoulders. Maybe that's just due to the decade of constant use though.