I haven't played 2015 (did play 2010-2014 though) but from the videos I've watched the AI looks pretty much the same as the previous games. They are way too passive and give up any position where you have the slightest bit of overlap. Pcars AI is nowhere near perfect either but at least they fight for their positions.
I'd advise actually playing the game before making a judgement.
The AI in F1 2015 are not easy to pass, When you think you have the job done, they pop up again and try to overtake you. They fight you until you are out of sight. They even crash into you and spin you off the road.
I usually find that lapped cars fight for position also, even when blue flags are out