Look in the window of the Windows Resource Monitor in the righthand column with CPU / Disk / Network / Memory, it show a very moderate network load, it is quite normal.
Than look in the window of the Task Manager and the Internet load is very large. My thought was that this was caused by an external source, because your system does not ask that much, hence maybe that other person.
Therefore I suggested to ask him to stop for a moment. If the load in the Task Manager goes down you know what is causing the high rates in the rest of the day.
Hope this helps