Undulated triggers, from my experience, seem to be highly aggressive. A buddy of mine managed to squeeze a red tooth niger trigger, undulated trigger, and queen trigger into a 75
gal. He hasn't really had many problems. He claims that the red tooth niger is the dominant trigger in the tank. I would assume that the clown trigger would most likely be compatible. But definately when keeping triggers together, tank size is extremely important. 150 liters (about 39 gallons) in my opinion is too small to keep even a single mature trigger.
HTH