I am running TFS 2015 and are using the Visual Studio Build Step. On the developemnt machines I moved to use Visual Studio 2017 so I also want to use Visual Studio 2017 for
You can use MSBuild task instead of Visual Studio Build Step, then specify the location of MSBuild 15.0:
In TFS 2015 the build steps and forward compatibility is only updated when TFS is updated. If you are using TFS 2015.3 already then you will need to move to TFS 2017 to use this out of the box.
The build step ultimately calls out to devenv.exe and the drop down changes the path. You can call out manually to VS 2017...