This is just an application that manages the modem attached to PC. If the device is slow in terms of browsing speed, then there could be a couple of factors that cause this:
Reception. Make sure there is clear reception, and that you're in an area where the modem can connect, or you have enough service to connect.
Internet limitation. Sometimes you deplete the Internet data that was assigned to your contract, and the speed automatically decreases.
Carrier's infrastructure. Contact the carrier support assistants and explain that the device is slow, and the Internet speed can't be used in the current state, maybe they have a maintenance.