To open the Network tool, open the Diagnostic Tools window in Visual Studio 2015 and in the Debug menu, select Start Diagnostic Tools Without Debugging (or just press Alt + F2).

On the diagnostics page, select "Analysis target" (your launch project is pre-selected as the analysis target, but instead you can target the installed or running application), then select "Network" and click "Start". Alternatively, since this tool is part of the Performance and Diagnostics hub, you can also select additional tools to start a combined session.

https://blogs.msdn.microsoft.com/visualstudio/2015/05/04/introducing-visual-studios-network-tool/