Seems MotorKing (Jay, the Fram rep here) said they (Fram) have found that the Ultra could easily handle the 15,000 mile interval, and found even 20,000 miles was not a problem, so they changed the numbers, but nothing inside the filter itself changed.
Current Ultra with 15k on the box can be used for 20k if you so choose. Several examples here of them going that long before the box changed.
And before anyone says it, no, Fram probably would not warranty an Ultra with 15k on the box (they could check by date code) that caused an engine problem @ 18k miles, but is that really an issue?
I think it is a good thing. Many manufacturers are going to a 10,000 mile OCI, and some still also recommend changing the filter every other change, so this allows the Ultra to meet OEM intervals.
But then again, if OEM says it is OK to do 20,000 miles on an OEM filter, shouldn't all filters be able to handle it?