Yesterday I have experience that I tried to install NuGet Package but an error occurred while retrieving package metadata in Visual Studio 2015.
After getting some try and catch. I found out that the VS2015 is configured to connect the API v3 of the NuGet.org. So I tried to add another one with the URL on API v2 of the NuGet.org and I am then able to install any NuGet package. So I think that if you hit into the same error, this is a good to try.