I have recently upgraded from VS2012 RC to RTM, and since the upgrade to RTM, I can no longer access nuget. I receive the following error in the Manage NuGet Packages window.
NuGet VS 2015 ServicePointManager does not support proxies with the https scheme
Problem was not with proxy because the proxy was removed in my case. Therefore the visual studio config file had to be changed. But in other cases the answer can also lie in changing the config file to your situation.
Go to: C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE
find the config file devenv.exe.config
and edit in administrator mode:
setting enabled="false" or adapt the section to your needs.
Restart VS after changes.