Is it possible to use postsharp with Visual Studio 2015 Express ASP.NET VNext projects? It seems that postsharp is not triggered on vnext application build.
PostSharp is integrated with msbuild toolchain out of the box. ASP.NET vNext comes with it's own project file format and doesn't use msbuild at all. So there is currently no easy way how to use PostSharp with ASP.NET vNext.
There is a working prototype for that so it is at least possible but it is far from being releasable and there is no official release schedule yet.
But you could try to increase pressure by creating a request on UserVoice:)