Unhook everything in your house that uses the router. Phones, computers, streaming devices, unhook it all and see if the PC runs faster. If it does, then you know one of the devices you have is eating bandwidth. (We just went through this and found a streaming device was the culprit.)
If the PC runs the same, then you know it's the PC. Time to check settings. Possibly update the firmware on the router, or update your Wifi or LAN driver.