I understand 17-15 would have made a slight difference at that time, (and I like how you assume he would have kicked that wide-ish conversion btw, given all kickers struggled on the night
), but if you've watched the ABs in recent times, you'll know full-well the main thing that sets them apart from other sides is the last 20 minutes, as they have proved time and time again in recent years when games are tight going into the last quarter, so I don't think psychologically it would have been such a big deal if they were down 17-15 prior to half-time, but sure, the final score-line might have been closer.
Also, on the other side of the coin, the ABs did hand Australia several opportunities in that first half by not looking after the pill, and of course Barrett is proving such a poor goal kicker at this level, which also cost us 5-7 points at half-time.
I do think Australia have made some slight progress since the English tests at the beginning of the season, but not sure it will be enough to turn it around to beat England at Twickers. Should be interesting.