You mentioned earlier that your basis was $1,000,000 so your realized gain on this deal is not going to exceed the FMV ($15,000,000 that you received for the property you relinquished) less your basis of $1,000,000.
Thus, your realized gain would be $14,000,000 (the same as if you had not done an exchange).
I suspect the confusion here is the result of the specific fact pattern, which involves a replacement property that has a FMV less than the basis of the relinquished property ($400,000 v $1,000,000). There does not appear to be any real tax benefit in that scenario and that is precisely what @Mike9241 was stating in his post.
