>>Gives 2.1544 - meaning that $100, with interest of 5.25%, would accrue $115.44 interest over fifteen years. Which then means that anything paid over the calculated installment saves you 1.15 times as much in interest that will not be charged over the next 15 years; 1.04 over 14 years (i.e. whatever you pay extra in the 2nd year) etc. Anyone can calculate interest, it's not quantum rocketology.
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>>But people are lazy and gullible (which is the same - lazy to think).
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>I really don't think that's the issue at all. Most people simply don't have enough savings to pay off a mortgage that quickly.

One does not pay off a mortgage from savings - savings have gone into down payment and closing costs. It's from current income. The more you pay to yourself (which is the debt repayment, essentially), the less interest you pay. There are three things which influence the total interest: size of principal, rate and length of time. The rate is more or less out of debtor's hands; the other two one can control.

And I'm not talking about those who really can't do it. It's about those who can, but didn't even think about it.