These are a great exercise , because you only have 15 minutes. So you are always thinking what is truly important about an image and how can you capture it as quickly as possible. You don't get hung up on the details , and start realizing how simple and broad brushstrokes can describe far more,usually with a better aesthetic touch than relentless rendering. You also learn to let go and move on to something else...which obligates you to try and get the damn thing right the first time!
Here are some of the ones I like the best and/or learned the most from, side by side with the movie stills I studied them from.