As mentioned in "Git support for Visual Studio - Git, TFS, and VS put into Context", Visual Studio uses libgit2 for Git support.
And libgit2 only got ssh support in May 2013 (PR 1558, libgit2 v0.19.0+), a bit late for VS 2013.
VS2015 should include a more recent version of libgit2, but ssh support wasn't yet planned.
See "Visual Studio 2015 CTP 6 and Team Foundation Server 2015 CTP Released".
Saeed Noursalehi [MSFT] 4 Mar 2015 4:45 PM #
We have no immediate plans to support SSH
There is an issue pending.
This discussion has been gaining more steam internally.
I don't have a date yet, but it's something we'll take a hard look at in our next round of planning.