You might want to consider walling off a 3' x 6' section for a veg room. You can put in a shelf, grow clones on it and veg plants below. You can light the veg area with a 400 watt Metal Halide or a big T-5. For this size, a T-5 would probably be best.
This would leave you with a 9 x 6 bloom room. I like zems rec. Except, if you do the veg room, you can get by with just 4 600 watt HPS.
As far as yield goes, this settup can give you 2lb/crop easy. I have a friend with a 4 - 600 watt HPS settup and he gets 5+ lbs on every crop of Bubba. This will take you some time to work up to.
I know you're thinking lights right now, but don't forget atmosphere. 75 degrees and 40% humidity. People will tell you 50%, but I've found that 50% can give you powdery mildew problems. Before you bring in any plants, put the lights on a timer and take min/max temp and humidity readings. Add exhaust fans, dehumidifiers, and maybe air conditioners until you get it right. Once the atmosphere is perfect, bring in the plants. It's hard to work on atmosphere equipment with a room full of plants. Oh...don't forget your odor control.
Good luck. You have a great space. I look forward to seeing what you can do with it.
https://www.rollitup.org/indoor-growing/407048-20-000-watt-medical-grow.html