Just upgraded to Windows 10 and VS 2015.
On a basic UWP app with some nuget references the building process takes almost 1 minute. It stays mostly at "1> Generating native code"
Then to create store packages it takes even longer, about 5 minutes.
Microsoft Visual Studio Community 2015Version 14.0.23107.0 D14REL
Microsoft .NET Framework
Version 4.6.00079
Regards