I think Primal's image hosting service is massively capped on the number of simultaneous connections. Images on fresh posts (< 2mins) take forever to load because so many people are downloading at the same time. During that time, even if you open the link on the browser, it takes minutes for a 3MB image to load. If you let it pass a few mins, it comes back to normal speeds.

Nostr.build doesnt seem to have that problem.