How do I disable C# 6 Support in Visual Studio 2015?

Question

Background

We have a project that we\'re developing in VS 2015 with C#6 enabled that occasionally needs to be opened by developers using VS 2013 without C#6.

Answer 1

Steps have already been written above, just adding a screenshot further of my VS2015:

Properties of project >> Build >> Advanced >> Language version

I set that to C# 5.0.