You should be able to install this update on top of previous installations of Visual Studio 2015. You can also access the bits and release notes right now on an Azure-hosted VM.

To learn more about other related downloads, see the Downloads page. Otherwise, you may have to restart the computer after you apply this security update if a file that is being updated is open or in use by Visual Studio.

We recommend that you close Visual Studio 2015 before you install this security update. However, in some cases, you have to install the two packages separately. Typically, KB 3165756 is installed automatically when you install Visual Studio 2015 Update 3. To apply this security update, you must have both Visual Studio 2015 Update 3 and the subsequent Cumulative Servicing Release KB 3165756 installed. This article helps you resolve the 'This update requires Visual Studio 2015 Update 3 to be installed' error that occurs if a required cumulative servicing and performance update (KB3165756) to Visual Studio 2015 Update 3 is missing. Microsoft Visual Studio 2015 Update 3 Security Patch

Visual studio 2015 update 3 download