As requested by OP, not sure if it's an answer - but there doesn't seem to be a better one at the moment, unfortunately...
This may be helpful, this is a User Voice for this and still unresolved as it seems.
As per the @HenkHolterman's comment - that I agree with - I don't think that's a snippet. For the moment it seems to be built into VS (out of curiosity I searched through VS 15 - new version not the 2015, and nothing new in there either - I searched all files for anything resembling XML comments).
There's a VB solution that, as I could see, places a custom .XML file in the specific AppData location - which doesn't work for C#. They describe the process as...
Visual Studio has built-in defaults for the XML skeletons that get
inserted, but when VBXMLDoc.xml is present upon startup, Visual Studio
will use the XML definitions from that file instead