Why do need to make $400k a year "for decades" to pay a $1.5M home down to a level at which a significant income change doesn't evict you? With some napkin math, let's say down payment was $200k, so you have $1.3M loan, and if you pay down $100k a year then after just 8 years you are down to a mortgage of $500k. Still a lot of money, but won't get you evicted if you make less, and while on $400k a year and with a spouse that has income too, you shouldbe able to reach that even earlier.
That's a lot of handwavey assumptions about how much you can pay off per year / month; where's that $100K pay down coming from? How much is the interest pay? What other expenses are there?
