No, a 15-second video isn't monetized the same way as a 15-minute video. Once a video gets to the 10-minute mark, you can add another ad spot to the end of that video and even add ad spots within the video. From a monetization standpoint, it makes no sense to make a video shorter than 10 minutes. And while it is debatable about whether or not and/or how one should insert ads within a video, there is really no debate about putting an ad at the end of the video. The end ad turns off no one and can generate revenue for you.