You didn't think that through, did you? It's longer than 15 seconds.

Isn't that the real problem? You're a company that says "here's 15 seconds to convey some information". Yet, you aren't able to convey the information you wanted to (i.e the ad for your service) in 15 seconds. I think they missed a trick with this ad.

Alternatively, Instagram didn't think their messaging through. 15 seconds is a long time.