This position is superior to the alternatives, in my view. All of the related passages in Scripture can be best harmonized with this explanation, and one does not have to treat the references to 400 years as a rounded number or the reference to four generations as non-literal. Furthermore, this view prevents one from having to assume any gaps in Moses' genealogy in Exodus 6. Finally, the 215 year duration fits well with secular history. Though these dates are debatable, a case can be made for the years in Egypt from Jacob to the exodus spanning 1662 - 1447 B.C. The main objection to the above explanation is that some believe it to be mathematically impossible to increase the population of the Israelites from less than 100 males to over 600,000 men in 215 years. But, though the population numbers are challenging, they are not impossible considering that God blessed them with swarms of children (cf. Exo. 1:7).
Let's do a little math together:
If we start with just 32 young males (i.e., grandsons of Jacob) at the time of the migration (cf. Gen. 46), and propose that each one of them would have 5 sons on average in 32.5 years, we would have 160 young males after 32.5 years. If this rate continued, we'd have 800 young males after 65 years. We'd have 4000 young males after 97.5 years, 20,000 young males after 130 years, and 100,000 young males after 162.5 years. Finally, after 195 years, we'd have 500,000 young males. At 215 years after the migration, Moses led all the Israelite nation out of Egypt. These 500,000 young males would all be men at that point (20 years of age or older) and most of their fathers would have still been alive (100,000 men). There were certainly grandfathers and great-grandfathers who were still alive as well, but we don't need to count many of them to harmonize with Numbers 1:45,46 - "So all who were numbered of the children of Israel, by their fathers' houses, from twenty years old and above, all who were able to go to war in Israel--all who were numbered were 603,550." 500,000 + 100,000 + some grandfathers easily gets us over the census number recorded after the exodus. Likely there were fewer young men and more older men in actuality, but the math above presents one possible way to get to 603,550 men.
And now, for the objections:
It should also be noted that we only assumed 32 young males initially for our calculating purposes. It may have been more than that, though it is impossible to know for certain how many of those listed in Genesis 46 were actually born prior to the migration (cf. our archived lesson from 06/30/12 for an explanation of this). I mention it at this point only to observe that if the number of initial males was increased, it would result in an average of less than 5 sons being required per male. Furthermore, the following conditions would also get us to the desired number:
Admittedly, much of the population figuring above is speculative, but as long as we have something feasible we can put to rest the challenge some raise about 215 years being an insufficient amount of time for the Israelite population to grow to over 600,000 men.