AC Unity, horrible lag

Hi, so Ubisoft recently gave away AC3. I played it and liked it. Runs very smoothly at hingest settings. Decided to buy Unity and boom. Even at 800px resolution and lowest graphics even mouse at start screen is lagging. Every key press has 1-2s pause before anything happens.

Its impossible to play it. (I just mailed Ubisoft if I could get my money back, doubt it). If I do I might remain as a customer, if not wont touch their games again even with a long stick.

Has anyone else similar problems? Running on custom built Windows 7 PC that should run it just fine.
Also directly after downloading whole PC seems to be very laggy. Wtf?

I really don't want to mock you but seriously are you comparing ac3 to unity(graphically) i played ac 3 on radeon 6480g and unity is a high end game really high end plus it performs horribly even on a gtx 1080p it's not ported for pc that well as ubisoft make shit games for pc now if your pc is good then it will surely run it otherwise apply some tweaks and lower all settings disable shadows