My problem was solved this way:
1. Open IIS Manager
2. Right-click on Default Web Site, Manage Web Site, Advanced Settings...
3. In the window that opens, expand Connection Limits
4. Go to Maximum Bandwidth (Bytes/second)
The value should be at least 10 million (10000000)
5. Click OK and the speed should immediately increase.
If you have a fiber optic Internet connection to the server, make it a billion.