Mobile phone internet USB tethering very SLOW I have galaxy s6 edge+
My download speeds on my phone is 33+mb/s with my mobile carrier.
I connect the phone to my PC and use the internet from the phone with USB tethering enabled.

The download speed is now 30kb/s on my computer but still 33mb/s on my phone.

Why has the speed been very limited via USB tethering, and how can I fix this issue?

I have tried changing/updating the USB tehter driver via Device manager to the Microsoft:

Remote NDIS based Internet Sharing Device

and

Remote NDIS Compatible Device

neither helped.
Mobile network carrier often have transparent gateways installed all mobile network traffic have to pass. Such gateways are able to "detect" (smart guessing) if traffic comes from the Smartphone or a tethered PC. 

Depending on the data plan contract, tethering may be prohibited and in such a case the carrier can just forcefully slow down the tethered connection.

As only the tethered connections are slowed down you can end up in a situation where identical downloads get a totally different download speed.