Thank you for the post.
It is not easy to find the root cause of the slow copying issue but there
are some suggestions you can try:
1. Contact your local Microsoft Service to obtain and install the hotfix
2. Unplug your external USB devices
3. Temporarily disable the Windows Search service to test the result.
4. Disable the "Remote Differential Compression" feature in "Turn Windows
features on or off".
5. Create or modify a DWORD value as 1 for
Hope it helps.
Tim Quan - MSFT