Having installed managed ODP.NET on my computer, the ODP.NET Managed Driver does not appear inside the Choose Data Source dialog in Visual Studio 2
I has same error. Since I installed vs2015 Update 3.
solve Reinstall Oracle Developer Tools for Visual Studio 2015. http://www.oracle.com/technetwork/topics/dotnet/downloads/odacmsidownload-2745497.html
ref https://community.oracle.com/thread/648192