Keep doing the current active TZ, when you draw two fairly quick in it. Do all of the acts.
Last 3 times I did full games this way it's been between 20-23 heralds per game.
Usually takes me about an 1h50min on warlock. a bit slower on some other builds
My average is also around 15-22 ish (hammerdin, warlock is too $$$ this season for me) that's good advice tho, just keep remaking games until you hit 2 ire's in 1 go then start clearing acts.