Do some reading on SOG. Here's a link to get you started.
http://www.dopequest.com/growtips.htm There's a menu listing but the quick links aren't work so if you scroll down about 1/5 of the way you see the subject: Sea Of Green.
The 150s are definitely an improvement. And, no, you cannot put a mh bulb in an hps light. The ballasts are different.
~Worm