15kWh is about the same as 6 of your 12V 206Ah batteries so you definitely didn't mean 15kWh.
15Wh is about what you might use running a few LED lights for about 4 hours so you definitely didn't mean 15Wh.
1500Wh (or 1.5kWh) would be about right since that's 28% of your battery capacity.