Hi All,
After searching for a solution to this problem today, I discovered that "Visual Studio 2105 Community" no longer includes C++ as part of the install. It only installs for C# and Basic by default. At the start of the install process choose the "Custom Install" option rather than "Default" and tick the "Language C++" check box (It will also select the relevant sub-items for you). BTW. When you choose the "Custom Install" option it also installs the "Default" options as well.
After restarting my PC, the Stencyl IDE was able to see it and compile my game for Windows.
PS. I am running Windows 10 and Intel i7 CPU.
Just another suggestion for anyone having this problem.