The issue sounds like the PC stops sending the information to the MFP rather than the MFP dropping the PC.
If the Printer was dropping the PC's it would drop all of them, not one.
With that in mind I would look into the Wireless/NIC settings on the PC end.
First step is to make sure that Power saving in Win 7 is not set to put the NIC to sleep
For reliability you could also create an address book entry to the device with the SMB/FTP scan information so there would be no chance of dropped connections. No software means no resetting.
The latest Firmware for the 3315 is 52.005.23.000 and dated 09/14
The latest for the 3325 is 51.005.24.00 and is dated 12/14
You would need to call Xerox to get those 2 version as they are not general release, just call for 2nd level support and ask for the latest spar firmware.
For Xerox to develop a firmware they would need to be able to replicate the issue, They would need detailed recreation steps and all applicable PC settings and the version of the software you are using (1.02.17.00(1/11/2012 is current)
Extremely helpful would be a wireshark trace between the PC and MFP as the issue is happening including the reconnect (Just remember, do not post the wireshark here on a public forum)