I have a 2x3 closet and run a 250. with a 4x4 closet, I would EASILY go with a 400 or 600 watt.
Do a search for Sandiegojack on here. He has a 4x4 room and runs a 1000w light and gets MASSIVE results.
In short, yes a 150 would work, but I'd stick to 3 or less plants.
Grab a 400/600 and you'll...