After installing Update 3 for Visual Studio 2015, I suddenly got the "This project is incompatible with the current version of Visual Studio" error message while opening my Cordova project (.jsproj Javascript project file)
To solve this:
Go to Programs & Features
Select the Microsoft Visual Studio 2015 installation and click Change
Click Modify
Install "HTML/Javascript (Apache Cordova) Update 10" of the Cross Platform Mobile Development section