I'm no expert on this, because that's not my style of growing, but from what I know about lighting and growing in general, sounds to me like you have a realistic framework. With the right strain and the right pheno, 30 lbs isn't unrealistic. Not a slam dunk, but you probably wouldn't be spending this much front-end coin unless you feel pretty sure you know what you're doing, so I'm going to assume you do.
How high are those ceilings - how much headspace do you have to work with? How do you plan to vent the lights? The exhaust from 15K watts would make a plume that helicopters will see from Australia if it's not concealed somehow. Have you thought about that?
What's your medium, and your plan for watering/feeding and drainage? Does the floor slope?
Again, for choppers.... are you concerned about the infrared signature from the walls of the garage, or do you think the AC will keep the air temps stable enough? Even so, you would quite possibly have hot spots or hot zones near the ceiling due to all those 1K HPS bulbs.
What about odor control? One problem you sometimes see with large garage grows is that the garage doors aren't really very airtight, and odor can get out under and around them. Not usually a problem if nobody comes near the garage, but there's always the mailman, the UPS guy, the meter reader... or just a neighbor walking over to say hi.
What's your electrical supply situation? You'll be drinking lots of electrons. You don't have a smart meter on that new house, do you?
Good luck. Sounds like a lot of fun. All your house payments in less than a year. Way cool!