Updating video drivers in boot camp
If you've already reinstalled Windows 10 on your Mac then be sure to download the latest Windows support software from the Boot Camp tool to ensure you have the latest drivers.As of April 2016, AMD has finally released an updated Radeon Boot Camp driver for the 2015 Mac Book Pro Retina 15″ and similar i Mac Retina models.A good example is the trackpad which simply doesn’t operate as smoothly as under Mac OSX.
With Apple's continued support of Boot Camp for Windows 10 we should see updates in the future to address any trackpad issues or battery life problems that some Mac owners have noticed after installing Windows 10.
This updated driver fully supports Rainbow Six Siege and other new games.
I recommend you use this supported driver at this time.
If you have an existing 32-bit installation of Windows on your Mac, you'll need to back up your important files so that you can remove the existing Windows partition and install a 64 bit version of Windows.
You can install Windows 8.1 on an internal drive in your Mac.