(For Treacherous Ground vs Firing Line). When you want to Ulti, try dropping Warder's Field first, to try and bait Khan into using his Shout. Once he's used it, wait 4-5 seconds, and then Ulti once the CC immunity has worn off.
If you use Agony, stun Torvald whenever he's preparing/starting his Ultimate. He is not CC-immune during his ulti, and stunning him will stop his Ult and can save your teammates from being thrown off the map.