Sorry but I don’t think it returns 10%. It looks like you get a 10% DISCOUNT, meaning you only have to pay 90% of the original price. The interest is 1.912% semiannually (twice a year or once every six months). If my math is correct, by Feb 3, 2020, (three 6-month periods, unfortunately it's too late to get four), you’d end up with 15,860 if you invested all of the 15,000. That’s not including the 10% discount, so you’d actually get a little more. Wait for someone else to confirm or correct my math, though.
It’s VERY DIFFICULT to get a guaranteed rate of return over 3% if we’re talking about investments in a short time period (as opposed to money you’d SAVE by paying off a debt that you owe, like a car or student loan of 5%).
Good job for asking these questions at your age!