That’s kind of tricky. The usual problem we see with network bandwidth is not the local network within a site, but the WAN links connecting sites to each other; there, the answers are usually to either deploy more relays to local sites, or use PeerNest to share downloads between clients so fewer of them cross a WAN link to do the download.
If your local networks are the problem, and not the links between sites or between switches, then adding PeerNest might actually make it worse.
I’d probably look at Bandwidth Throttling on your in-site Relays at the slow sites. Referring to List of settings and detailed descriptions I’d probably start with _BESRelay_HTTPServer_ThrottleKBPS and limit it to some bandwidth you think your switches can handle ok. This setting limits the download speed that the Relay will support when clients are requesting files from it. That’s probably the easiest place to tune it.