Scott,
TBH, I think since you are going from VHO to MH, you might be better satisfied running 20k bulbs. I'm not sure what type of livestock you are trying to keep, but your tank is pretty shallow, and I think you could get by with 175 20k's for the stuff I think you like to keep. Just keep SPS near the top.
JMO. But let us know how you like the 15's. I've personally gotten used to the bright whote from the halides and sometimes washed out look some of my corals develop.
