I have just downloaded boost 1.60 for a regular update, I have found some kind of build problem with my environment (vs2015 update 1 with Windows SDK 10.0.10586.0).
I usually just do this to get a build:
call bootstrap
b2 headers
bjam --build-type=complete --toolset=msvc-14.0 -j13 address-model=64 stage
I have never required vcvarsall.bat as boost build allways finds its way. However today it wasn't able to find my windows headers so I manually did this:
%comspec% /k ""C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat"" x86_amd64 10.0.10586.0
Even so I found that boost was looking for sdk 10.0.10240.0 (an older one). In my system I still had that sdk directory, however it only contained some UCRT stuff.