Optimization in new DLC zones is plain horrible.
Stirring at single surface (with geometry behind) drops FPS to 40. Stirring at pillars and sky above rises FPS up to 90.
Plain wall with scenery behind it:
http://i.imgur.com/4ixtydx.jpg - 40 FPS
Stirring at sky and pillars (many more visible polycounts, a lot less geometry actually rendered):
i.imgur.com/RT4q3eU.jpg - 88 FPS
You can see it's same spot thanks to compass markings. No settings changed.
The fact that the game will probably have DX12 update in future doesn't mean that you should skyrocket draw calls in every place possible. I've a feeling that HOMs update will come to PC when the DLC is released to consoles. Gotta check HOMs in Orsinium.