@surfboy sorry for late reply!
I've had even worse problems lately, so I am doing some troubleshooting; image speeds fall down to 1 GB / min, imaging lasts about 15-20 minutes. I have spare SSD 2.5" drive, SPPC, I've disconnected NVME, put SSD in and put image to that SSD drive - speeds are as expected, around 5.5 GB / min.
In desperation, I've created image with Aomei Backupper, which works through WinPE boot disk, and it works great. Speeds are around 120 MB / s, which was expected from cheap USB3 device, and it took around 5 minutes to finish.
So, linux drivers / support for NVME is the problem here, not network.
@theopenem_admin can something be done about that? WIE is currently not an option, unfortunately.