Here is a simple CMakeLists.txt file:

cmake_minimum_required(VERSION 3.6.3)
set(CMAKE_SYSTEM_VERSION "10.0.17763.0" CACHE STRING INTERNAL FORCE)
set(CMAKE_VS_WINDOWS_TARGET_PLATFORM_VERSION "10.0.17763.0" CACHE STRING INTERNAL FORCE)

project(SimpleProject)
add_executable(SimpleProject "Source.cpp")

For some reason, if I generate with cmake . -G "Visual Studio 14 2015" -A Win32, I see:

<WindowsTargetPlatformVersion>10.0.10586.0</WindowsTargetPlatformVersion>

In the build it also says:

-- Selecting Windows SDK version 10.0.10586.0 to target Windows 10.0.17763.0.

If I generate a VS 2019 project instead, it works correctly. Why wouldn't the same work for 2015? I can manually change it once in the IDE to match the SDK version I'm trying to use, but can't seem to do it from CMake. Thanks!