15GH/s seems like abit crazy, and I think it is well worth the money invested.
ROI will depend on your electricity bill as this miner required 1200W.
it's 1000W and 17.2GH for the shipped units
These are even better specs than advised. Less electricity consumption= more benefit.
I think the D3 from the november batch will pay off itself in maximum a month, afterwards you're only making profit, 1000w is really not that much.