If it’s a bunch of users sharing a bunch of resources from behind a bunch of different VPNs, I guess the most simple way is to tell them to expose it to the internet

Are you sharing your Linux PC with a bunch of different users? Or are you sharing your Linux server with a bunch of different users?

It’s not a factor for me, but if you continually find slow speed you could try picking a mirror that has better perf. Also dnf can be incredibly slow so you may need some additional max_parallel_downloads tuning