OK, so if you were actually experiencing a 3A average load, you would be using 12Ah per 15 min flight. I think something isn't being reported correctly or maybe is being misinterpreted from the logger. Anyway, this is just a matter of getting terminology straught. At least you confirmed that things are running normally.

Sorry for getting things off track a bit, this is derailing the question of whether to use one pack or two. I would always go with two for anything I care much about. I recently did a pair of 2M pattern birds with dual LiPo's each. Of the 4 new LiPo packs I bought, one had an intermittent connector, right out of the package. It was a problem with the way the wire had been crimped to the connector pin. It worked most of the time, but in my normal bench testing, I caught it. Even so, it could have easily gone into an airplane and caused a crash if it had been a single battery setup. Murphy is there all the time and I like to go with some backup to try to defeat him.