Don,
With that HT/HS viscosity, I'd say 15.3 looks about right for an SAE 5w-40. For example, the AFL product is 13.7 Cst and the HT/HS is 3.7 Cp @ 150C. As I anticipated, this is a variation of the additive chemistry you first saw in the new "AFL" European oil.
If you do a VOA of this oil, you'll find the same level of calcium/magnesium as in their European formulation, but the zinc/phosphorus levels will be 20%-25% higher. I'd guess 950-1000 ppm of P and 1100-1200 ppm of zinc.
Note that ZDDP contributes about 10%-15% of the sulfated ash in a fully formulated engine oil, as well as some sulphur. So even though the CJ-4 spec allows 1200 ppm of phosphorus, you're going to see less in these new CJ-4 formulations. If you went with the max levels of ZDDP, you'd have to drop the Ca/Mg (TBN) even lower to meet the SA limit.
By the way, this should also be an excellent oil for older domestic gas engines or European engines requiring a 5w-40.
TS