Get the Libpack https://github.com/FreeCAD/FreeCAD/rele ... 64_VC15.7z
Extract with .7z where you want
Get CMake https://cmake.org/
Start the CMake-Gui, set the path to the source dir and build dir.
Run Configure, make sure you set the VS2015 generator and the bitness x64, it will fail.
Set the FREECAD_LIBPACK_DIR to where you placed the Libpack
You may need to set BUILD_QT5, if it's not set automatically, set it.
Run Configure, it should work, run Generate, close CMake-Gui
Double-click on FreeCAD.sln in the build folder.
This should open the VS2015 IDE, make sure Release and x64 are selected in the tabs at the top of the page.
Then Build > Build Solution
When this is finished, close the VS IDE, copy the contents of the Libpack/bin to build/bin
Start FreeCAD from the FreeCAD.exe in the build directory.