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.

Looks like today everything go faster without fails. I don’t know if they applied the PR from Lemmy.world but today the performance is great! Thanks!

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