Hitman launched with DirectX 12 support, so it was strange that Hitman 2 didn't. IO Interactive finally added support March, which has boosted frame rates on higher-end systems, and the studio is working to make it better on low-end rigs, it said this week.
In a Microsoft blog post, the dev team said that users were reporting improved performance since DX12 support was added, and internal testing had showed an 43% improvement in frame rates. However, that data was gathered on a six-core Haswell CPU and AMD Fury X GPU—with lower-end systems, DX11 still offers better performance, and IO wants to change that.
"DirectX 12 requires additional work on the part of the game, so in some cases the overhead of this may result in poorer performance compared to the DirectX 11 version," it said. "We are still optimizing our DirectX 12 implementation and we expect to see improved performance on additional configurations, but currently DirectX 11 may be the best option for players with less capable systems."
It didn't say when we can expect better performance on lower-end machines, but I'd expect that it'll come as the team receive more feedback from players. You can read the full blog post, which contains details as to why exactly DX12 improves performance, here.