C# 6 Isues?

When trying to build a sln (wich works fine in VS) I get "Error:(366, 51) CS1056: Unexpected character '$'" reffers to a location where C#6 string interpolation is used.

Build output:

Microsoft (R) Build Engine version 4.6.2001.0
[Microsoft .NET Framework, version 4.0.30319.42000]
Copyright (C) Microsoft Corporation. All rights reserved.

Settings > Build, Execution, Deployment > Toolset > 4.0 Or higher.

Edit: Fixed it..
Downloaded Microsoft Build Tools 2015, and changed the Toolset to 14.0 Or higer.