Ensure 2015 is fully patched and updated. Restart Windows.
There are free add-ons from the AutoCAD Exchange website that will do a lot more than regular AutoCAD PURGE command, grab and install one or both. One is called RADICAL PURGE and the other is called DWG PURGE.
Now.. Close AutoCAD, place this one file on your PC's desktop. Rename it. Disconnect from your network by unplugging the cable. Open this file in AutoCAD: what does it start complaining about and whare are your file content? I suggest you purge the file and all the unreferenced xrefs with the add-ons I mentioned.
Ensure all the XREFs got unloaded. Reconnect to your netowrk. Now open ONLY the other XREF files in your list of xrefs (do not open the original copy of the DWG file with the problem) and find out which of those, if any, has your top file xrefed in it. Remove it from each DWG file if found.
Now remain your original file, place the copy back, open it and reattach all the other XREFs.
If you're not able to do any of that then I need a lot more info then, or you need to jsut live with it, as I am unable to XREF a file into itself no matter how hard I try: see below, each color ought to be it's own screenshot(s).
