I am sure the same way everyone else who flies to Australia or NZ in economy does it. They make the best out of the situation, get up and move around when they can, and sleep if they can sleep. It's really not that terrible. You sit in the office for 8-10 hours a day. At least here, you can drink your brains off, watch movies (although not on UA it seems) and look out of the window. Not the best possible way to spend 15 hours, but you are in Australia by the end of it, and that in itself is worth it!
(people used to fly over the course of 7+ days not that long ago with a high probability of crashing and dying on some exotic island!)