This could be complicated by the fact you need to log into the wif in the first place. The college may be creating registry keys to do the timeout, or their own wifi is checking for activity on their own network to keep it alive.
So, if the college wifi has a timer to check network traffic, but only "valid" traffic, they may have a timer that you cannot do anything about...
However, if your system has some keep alive timer setting in registry, it may be set by either the login to wifi or the VPN software itself.
The common keep alive timer for TCP/IP V4 is located at:
HKLM\SYSTEM\CurrentControlSet \Services \Tcpip \Parameters\
but it may or may not exist. On my system, it does not - I have no timers...
However, if the VPN software or something else is creating it, you should be able to modify it, or try creating it yourself:
On the Windows server, click Start > Run and enter regedit.
To be on the safe side, make a backup of the current registry (File > Export).
Go to HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\ and create a DWORD called KeepAliveTime .
Right-click on the new DWORD, select Modify, and enter 7200000 (decimal) as the value.
Click OK.
Exit the registry editor, then turn off and restart the system.
That will set a 2 hour keepalive for TCP/IP V4
That all said, it could be other factors that are causing the timeout. Like I said, the college may have some smart firewall that does this, or your system has something set within the VPN software that is causing it, or even the VPN server you connect to may be bumping you off. There are just too many possibilities.
I would suggest trying a different VPN service, see if it does the same. You have to run out whether it is the actual VPN or something else that is timing out. If it acts the same, it has to be the college wifi login or your own PC that is disconnecting. If the new VPN service works, then it is the VPN service that was at fault.