Hi Gr
I have only suggestions for you
First try to avoid Alt-Tab or switch to other programs. GTR2 doesn't seem to appreciate such behavoir.
Second: possibly your problems aren't relatet to time (3 min), but to other players joining the server you're on.
So, join an empty server and see if the problem persists. If you loose connection then, check on Rennsimulanten-page if someone else has joined the server.
If so, it's a known problem, seemingly without solution and if not it might be your connection causing this.
Keep your files updated, don't switch to other apps and tell us what you found out.
Not few suffer disconnection problems, hopefully yours can be solved.
'Gr'eetings