The amount of data is 36 GB. I made a full backup in January. And it was fast enough. But recently the base was damaged and I could not restore it. I decided to make a new full backup. Now it It goes with some fantastically low speed. The process is already 20 hours but the progress is 0.00% and the speed is 50 KB/s.
Sounds like something is not right. I’ve found initial backups tend to run in the 5-10GB per hour range plus another 1-3 hours at the end for processing.
If the data is constantly in use elsewhere by another live/real time backup software, or security, firewall, antivirus, or something else blocking it could also be a possibility.
Thank you for your answer.
I make backup to S3 cloud storage Wasabi (like Amazon). I have upstream/downstream internet line 25 Mb/s and I expected to see even 5 GB per hour. I have no antivirus - only Windows Defender. No errors… and the speed is not depends of time. Day/night - from 45 to 60 KB/s. So - it is nearly 200 MB per hour 
My server is virtual Windows Server 2016, based on Hyper-V