There are multiple factors to this however there is not an exact/immediate way to speed up syncs however there are items to check. These checks and adjustments must happen on each end so each location that devices are housed at. Note that the ProMax software and hardware does not throttle speed of syncs. Most speeds are dependent on your network settings.
1. Open ports on each router for Sync to run specifically through the Sync ports. Please see document here on listed ports.
2. Run an iPerf test. These will need to run on all locations point to point.
3. Check how each device is connected via hardware and see if there are any network routing issues.
4. Check ISP speeds
5. Check where the sync paths are directed to. If there is an external drive with a spinning disk, this may limit the sync speeds as single spinning disk drives are much slower than RAIDs and SSDs.
6. Check if there is enough room on each storage device.
7. Check if there are any lingering Windows Updates. These can interfere with connections.