No, I would not feel safe working in a closed garage with an auto engine running for fifteen minutes. However, since I would be in the garage at the time, there is a fairly good chance that I would notice that it was running and turn it off.

In regard to the feature described vs. the Starbucks drive-thru, I suspect I would not be sitting in line stationary for 15 minutes. Even if I shifted in Park everytime the line stopped while a customer was being served at the window, the 15 minute clock would reset every time that I shifted into Drive to move up a spot in line. Unless I was at a Starbucks with unbelievably atrocious service, I would be surprised if the engine ever approached automatic shutdown. Even if it did, I would receive a warning message on the instrument cluster that a shut off was impending, and I could manually reset the 15 minute clock by pressing a button on the steering wheel spoke. Not even close to irksome.