As of today, March 11th, 2016, Rise of the Tomb Raider will implement one of the industry's first integrations of DirectX 12. This is great news.... really.
Steam users will automatically download the small 129mb patch and will expect to see some pretty big improvements in performance across the board. This doesn't mean that folks without Windows 10 can't play any more as DirectX 11 is still an option.
Grab the newest video drivers for your graphics cards to get the best performance as of yet. AMD users, make sure you choose the 16.3 hotfix driver suite.
I myself finally cracked and jumped on the Windows 10 bandwagon so I look forward to seeing the changes first hand.
And you can check out the dev blog post on the subject here