[Disapproval reason] Video ad length [What do I do now?] Non-skippable, TrueView in-stream video ads must be 15 seconds or less. Depending on the country or region in which you want to show your TrueView in-stream ad, the video can be up to 20 seconds long. There is no time limit for skippable TrueView in-stream video ads. [What does it mean?] 
Your ad goes over the allowed length of time.