Does DA:O works correctly with 2560x1440 resolution? I have DA from EA APP and I have very small UI with no possibility to make it bigger. I have 2560x1440 27' screen. Any one play on 2K resolution? Does Preservation Program fixed this?

No it doesn't scale correctly. You have to use a mod for it.

Your best bet might be to play it in 1280x720 resolution (which stil is native for your display and it is somewhere around expected resolution of this game as it was back in 2009), which will give you reasonably big UI - though it might be way too big (I am using 1280x800 on my 2560x1600 laptop and it is OK, but this is 15,3" laptop, of course, not a 27" display).

Some experimentation might be necessary, ideally with conjunction with UI scaling mod.