When starting Visual Studio 2015 for the first time, this takes quite some time. Also when opening files within the IDE this can take about ~2 seconds.
When using ReSharper be shure to run version 9.13 or higher – ReSharper ver. 9.1.2 was known to slow down VS2015.
Deinstallation of Node.js will also (dramatically) speed up your VS2015 IDE.