Why does the 15 seconds matter? My conversations with friends would be vastly different if I knew at any second they could push a button and get a transcript of what we just said. I'd pretty much never make a joke again.
Now imagine knowing that they'll go home and be able to see a nice summary of the various conversations throughout the night. Just very normal social behavior, made easy by Apple.
Lived without that for 5000yrs, don't need it now. It provides nothing except people no longer able to speak freely for fear. It's enabling a panopticon.