Well, probably, but considering that sh.itjust.works was targeted by bots, i suspect that it is slow not only because of the users
You can always switch to different, smaller instance (all posts and comments are available on all lemmy instances), but i'm not sure if there is any easy tool to transfer your subscribed communities
It's not due to poor hardware resources. The problem is due to low backend performances. I don't know if lemmy.ml is updated but the new patch will implement a lot of performance tweaks. For example, lemmy.world's admins found many huge performance issues and they made a couple of PR that have been merged so they will be available in the next release.
Lemmy.ml was just upgraded pretty substantially a couple of weeks ago with the first large reddit exodus, so unless there is a ton more monetary support from users, i don't really know that the problem will be solved. It's been like this since the 29th. Jerboa is all but unusable for me unless it's late at night.
Generally it is suggested to jump to a different instance and your performance may improve, lemmy.ml has been way overloaded for a long time