It is worth bearing in mind that the Near Eastern way of thinking about lengths of time and numbers in general is not as precise as ours.  For example, in Exodus we read that Moses was in the desert for forty years, it would be a mistake to take a Western/modernist approach and assume that the length of his sojourn in Midian was exactly forty years to the day.  Might it have been 44 years or 37 years?  Perhaps.  The number forty has symbolic meaning in Jewish literature, and it is possible that the length of time is rounded.

Therefore, I do NOT assume that the length of the sojourn can be determined precisely by any biblical estimate such as that of Paul.  However, I believe that we can decide which is closer to the truth–430 or 215 years.  The answer is that the sojourn in Egypt was somewhere near 430 years, but we should bear in mind that there is some numeric symbolism in the number of years, as well as rounding off.

You propose that there might be some need to reconcile Gal 3:16-18 with 430 years.  I am not sure what that is about.  Paul appears to be quoting from Exodus 12:40.  Both mention 430 years, so I am not sure why you ask for reconciliation with 430 years.  Even this Exodus passage leaves some room for interpretation, as the Masoretic Text says that Israel was  in Egypt for 430 years, but the Septuagint and Samaritan Pentateuch says Egypt and Canaan for 430 years.  What, exactly, does that mean?  Which is right?  If the 430 years includes some of the time that Israel (ie Jacob) was in Canaan, then the time in Egypt might be significantly shorter than 430 years.  Either way, it was NOT 215 years!  Some have even proposed that the 430 years includes the entire time from leaving Haran or from the youth of Isaac to the Exodus.  This would allow for only 215 years in Egypt, but this is almost certainly too small a time, given Genesis 15 and Acts 7 (see below).

It also ought to be born in mind that both Genesis 15:13 and Acts 7:6 mention 400 years.  Is the difference due to rounding (presumably, with the 400, rather than the 430 being the more rounded number)?  Or might the 400 years have a different starting point (such as when Joseph went down to Egypt verses when Jacob went there)?  Again, the experts have a number of explanations of this.

The exact length of time Israel was in Egypt is not important theologically.  For those who like precise answers, it might be unsettling to not have an exact answer.  However, the truth is that we will have to live with some uncertainty.  A lot of experts have thought a lot about the dates of going down to Egypt and of leaving Egypt, and they have never come to full consensus.  We should be skeptical of those who claim to have found “the” answer.  You and I are not likely to do better than the experts.

You ask my thoughts.  My thoughts are this.  Israel was in Egypt somewhere near 400 years, beginning from when Jacob went down into Egypt until Moses led them into Sinai, but this is an approximation, and it is the best we can do.  Jacob went down into Egypt somewhere around 1850-1800 BC and Israel left Egypt somewhere a little before 1400 BC. It so happens that this comports well with 1 Kings 6:1 as well.  Some have proposed a much later date, with Jacob going into Egypt in the seventeenth century BC, and Israel leaving Egypt in the 13th century BC. I am personally skeptical of these dates, but am open to being showed to be wrong.

John Oakes