I think that's called a "piggyback mortgage." Yours is an extreme example (sounds like you'll pay off the 15 year loan within a year) but generally used when yo

I think that's called a "piggyback mortgage." Yours is an extreme example (sounds like you'll pay off the 15 year loan within a year) but generally used when you can pay more initially because it's easier to pay off a loan early than to pay extra on your mortgage to get to 20% equity and end mortgage insurance payments. If you can get a low enough interest, the piggyback can be preferable (to PMI) even if you're not going to pay it off early, you just have to do that math.