That 150w halide will be at the center of 3 feet. So yeah, it all depends on what you're going to keep and where. All that aside, maybe 250w would be better for 24" height. But again like the last poster said, it depends on what you're keeping.
i have the same size tank and i had a similar fixture and in my opinion, the 150 watts wasn't enough light. I switched out to just one large lumenarc pendant with a single ended 250 watt bulb and all my corals are growing much better and my light bill is down significantly also.