C# 6.0 Features Not Working with Visual Studio 2015

I am testing Visual Studio 2015 with C# 6.0 but the language features are not working. In an MVC web application, the following code does compile:

if (!string.IsNullOrWhiteSpace(Model.Profile?.TypeName))
{
    // More logic here...
}

However, when I run the application via Debug and IIS Express, I get the following error:

CS1525: Invalid expression term '.'

How do I enable these features?