Approved by whom?
Castrol?
I think the only approvals that matter come from vehicle manufacturers, and even then, approval is contingent on the oil producer's willingness to pay for certification testing.
Looking at UOAs here of 10K runs of the two oils, there is only one for Edge. I found four for PP in the past year.
ZZman posted one from a Camry run just over 10K on Edge 10W-30. Wear looked very good, but TBN was shot at 1.5, so the oil could not have gone 15K.
In the case of PP, 10K in a Sentra yielded TBN of 3.0, 9649 miles in a Sky yielded TBN of 1.8, 10K in a Prius yieded TBN of 3.3, while 18K kilometers, near enough 11K miles, in a 3.3 liter Caravan yielded a TBN of 2.8.
If TBN is a good indication of when an oil is done, then I don't think you can say that US Edge is a long drain oil, while PP is not.
I understand that what I have posted above is not statistically significant, but based upon what we have to look at here, Edge has not distinguished itself as a better 10K choice than PP, much less 15K.
For grins, I went out to the garage, and checked PP, Edge, M1 EP and GC for approvals.
Edge, M1 EP, and PP, all in 5W-30 flavor are all API SM oils, while GC is an SL.
GC has MB 229.1/.3/.5, VW 502.00,505.00 and 503.00 as well as BMW LL-01 approvals. It seem that GC may be the real US-available long drain Castrol product.
Edge, PP and M1 EP list none of these, although PP meets Honda HTO-06.
Both Edge and EP claim on the bottle to be good for 15K or one year.
PP makes no such claims, although UOAs seem to bear out that it will hold up at least as well as Edge.
If anyone is interested, I could mine the UOA forum for 10K runs of EP and GC.
I would be curious how these two would hold up relative to Edge and PP.