Visual Studio 2015 is very slow

My Visual Studio 2015 RTM was also very slow using ReSharper 9.1.2, but it has worked fine since I upgraded to 9.1.3 (see ReSharper 9.1.3 to the Rescue). Perhaps a cue.

One more cue. A ReSharper 9.2 version was made available to:

refines integration with Visual Studio 2015 RTM, addressing issues discovered in versions 9.1.2 and 9.1.3

Try uninstalling either Node.js Tools for Visual Studio (NTVS) or the commercial add-on called ReSharper from JetBrains. Using both NTVS and Resharper causes memory leaks in Visual Studio 2015.

NTVS = Node Tools for Visual Studio

I found that the Windows Defender Antimalware is causing huge delays. Go to Update & Security -> Settings -> Windows Defender. Open the Defender and in the Settings selection, choose Exclusions and add the "devenv.exe' process. It worked for me

Try turning off the ReSharper Code Inspection from menu Options → Code Inspection → Setting and choosing Visual Studio IntelliSense (menu Option → Intellisense → General) instead of ReSharper IntelliSense will make it much faster.