slow
rsync is pretty fast, frankly. Once it's run once, if you have -a or -t passed, it'll synchronize mtimes. If the modification time and filesize matches, by default, rsync won't look at a file further, so subsequent runs will be pretty fast. You can't really beat that for speed unless you have some sort of monitoring system in place (like, filesystem-level support for identifying modifications).

https://gist.github.com/michelleeywao/b10f25152200040f291fd6c6d0d71329
This appears to be from three months ago. It sounds like Imgur can ban IPs
I assume that this is a tempban.
The above study lists success rates for requesting images on various VPNs. NordVPN is at 98%, ExpressVPN 97%.
It also says that free VPNs have a far lower success rate, as their IPs tend to be blacklisted.