I started my own channel recently, created 7 new short videos. After looking at my audience retention, Ive noticed my short 15-60sec videos have a score around 90-120%. But my longer 1+ min videos start dropping off at the 15sec mark. This one for example, http://www.youtube.com/watch?v=GTNpCsBxniM  gets up to 110% but then slowly declines to %50 at end of video. I just put an annotation at the 15 sec mark to get viewers more active about finishing video. Im not sure this will help, is there any tips out there to avoid this?

I know i just started and still barely have any views to really make use of the analytics but im curious.