July perhaps is the one of the most important month this year for Microsoft developers, at least this year. On July 20th, our most beloved IDE and development tool, Visual Studio 2015 will be released. On July 29th, the most awaited operating system, Windows 10 will be available. With the release of Windows 10, we will also see the releases of final Windows 10 SDK and Universal Windows App tools.
That means, when Visual Studio 2015 is released on July 20, the preview version of Windows 10 SDK and universal Windows App tools will not work.
I just read a blog post on Microsoft and Microsoft recommends, you should wait to install Visual Studio 2015 RTM until July 29. When Windows 10 is available on July 29, you can install Visual Studio 2015 and Windows Universal app tools.
If you do not wish to wait till July 29, here is an alternative method for that:
http://blogs.windows.com/buildingapps/2015/06/29/release-dates-and-compatibility-visual-studio-2015-and-windows-10-sdk/