According to Cfx support themselves, RedM downloads are P2P (peer to peer), meaning you are downloading the game cache from other players.
The reason for P2P is that Rockstar isn’t hosting old executable versions (like they do for GTAV), and it would be illegal for Cfx (or anyone) to host the RDR2 game files.
Since the game cache downloads are Peer 2 Peer, the speeds are depending on the number of other clients active and their respective upload speeds. Although it’s frustrating, it is normal for the downloads to be slow because of this. The best thing you can do is just kick off the download before you go to bed or go to work and let RedM do its thing. It’s like watching paint dry: just have to be patient with it.
As long as you have adequate free space on your C-drive, the RedM download will not fail. Before kicking off the RedM download, verify you have at LEAST 10% (25% free If you plan to do any screenshots or video capture) on your C-drive. I’ve seen some users RedM fail to download completely, after waiting a couple of hours, because they ran out of C-drive space. At that point you have to start all over again.
Rest assured: with a little patience at the beginning, you’ll be able to enjoy reading servers for months and years to come!
Here’s how to TEMPORARILY turn off your Windows Firewall to speed up RedM cache download.
NOTICE: Be sure to turn firewall back on after cache is downloaded!
Hope this is helpful! 