There are three version of USB.
Each version offering improved performance over previous releases. With each generation of USB comes improved data transfer rates.
USB 1.1 offers maximum speeds of 12Mbps
USB 2.0 offers maximum speeds of 480Mbps
USB 3 can deliver speeds of 4.8Gbps
You can find the version of your USB input via your device manager (Windows)
Google how to find the the USB input version to confirm which generation of USB input your computer has.
I'd say that's likely cause of the issue you're having. We do not throttle tethering speeds. I often using my phone has a hot spot and I've never had an issue.