Ok! I finally found the solution
The problem was related with old Project code (Binaries or Build folder)
so I reinstalled Android SDK ( 1R4u2 ) just for sure.
Deleted Project folders: Binaries, Build, Intermediate and DerivedDataCache folder
Generated Project Files, opened VS2015 and build the project again. worked like a charm 
In my special case I had to change my SDK API Level to android-22 due a plugin I’m using.
Hope this help’s someone with similar issue in the future.