I've calculated that the white race will go extinct in 72 generations
Assuming a population of whites of 850 million, it will only take 72 generations for a fertility rate of 1.5 to completely destroy the white race:
(.75^72)*850000000 < 1
I plug .75 into this formula because that's (1.5 children/foid) * (1 foid/2 people) = .75 children/person.
I'm assuming we count "total destruction" as whenever the number of whites drops below 1. There could still be some fractional quantities, but according to Hitler, as soon as you start diluting the white bloodline through miscegenation, cultural creativeness goes away pretty quickly, so for practical purposes, that means the white race is done at that point.
Even before 72 generations have passed, though, the white race will have reached a severe population bottleneck so that they'll only be able to reproduce through inbreeding. For example, after the 69th generation, it might be just one man and his daughter, so that he'd have to say to her, "Well honey, it's up to us to continue the white race." Ah, to be born in the year 3743, when there's the perfect excuse for father-daughter incest.
Well white guys, enjoy the days of being able to press your JBW advantage outside of the white world, because there's only another 1,800 years of that left, assuming each generation is spaced 25 years apart.