Debugging in decompiled assembly is not working in VS 2015

First, I created a testing assembly HelloWorld.dll which I want to debug and built it with release configuration.

namespace HelloWorld
{
    public class HelloClass
    {
        public string SayHello(string name)
        {
            return "Hi " + name + "!";
        }
    }
}

Then I created standart ASP.NET MVC project and:

- Referenced HelloWorld.dll assembly - Modified HomeController's About method

public ActionResult About()
{
    var testingClass = new HelloClass();
    ViewBag.Message = testingClass.SayHello("John");
    return View();
}

- Via .NET Reflector Object Browser decompiled HelloWorld assembly
- Put breakpoint inside SayHello method (in decompiled file)
- Run debug in IIS express or IIS and request ~/Home/About page
Result: Brekpoint is never hit.

When I go to Debug -> Windows -> Modules it seems that symbols for HelloWorld.dll assembly were loaded.
However, when I do same steps in VS 2013, everything works fine.

Thanks.

Visual Studio Professional 2015 - Version 14.0.24720.00 Update 1
.Net Reflector 8.5