These cumulative updates to Visual Studio 2015 include a variety of bug fixes and capability improvements.

If you have Visual Studio Enterprise 2015 installed on a machine with Internet access, Update 1 displays in the Notifications Hub. To install, select the Update 1 notification, and then complete the installation actions. You can also download Update 1 here.

Visual Studio Enterprise 2015 with Update 1 is an integrated, end-to-end solution for teams of any size with demanding quality and scale needs. Take advantage of comprehensive tools and services for designing, building, and managing complex enterprise applications and solutions.

Note: If you have installed Visual Studio Enterprise 2015 (original release version) and run this download from this page, only Update 1 is installed. If you haven't installed Visual Studio Enterprise 2015 and run the download, both Visual Studio Enterprise 2015 and Update 1 are installed. In either instance, Visual Studio 2015 Language Packs (original release versions) can also be installed.

VS Release Notes
TFS Release Notes
VS Known Issues
System Requirements
Compatibility