How do I use Qt in my Visual Studio 2015 projects?

Building

You can use Qt in Visual Studio 2015 without any problems. As already stated in the comments, you have to build it from source but Qt is pretty straightforward to build. You can download the current (5.5) sources here and then follow this step by step example on building it.

I would also suggest reading more about the configure options, this might save you a lot of time. It might possibly save you some external dependencies as well if you skip components you do not need. My configuration for instance contains -skip qtwebkit -skip qtwebchannel so I do not need ruby or python.

I could totally omit step 3 from the link. Just be sure to open the Visual Studio Command Prompt (32/64 is important here) for configure and nmake.

Usage

For Visual Studio 2015, the Qt Add-In is not available anymore. But there is an Extension (Tools > Extensions & Updates) called Qt5Package or QtPackage which has the same functionality. After installing it, you have the Qt entry on your main toolbar where you have to specify a version and the path to the directory where you built it. This version will also be associated with the current project via the same menu.

If you load an existing project, you also have to convert it so the whole Qt functionality is used automatically. You can do this by opening the solution and right click on it; there should be an entry for the conversion to a QtAddin generated project.

I am using Qt 5.5 on Visual Studio 2015 with an old project and it is working without any issues.

As of now, you can just download Qt for Visual Studio 2015. Here.