They like to use the "isosyn" label on the oil, but when you look at details, it is a conventional. My guess is they are taking advantage of the Group II+ classification. Not quite to the Group III, but not the standard group II either.
I am not sure why this particular oil is even being marketed. They already have 10w30 and 5w30 HDEO's in the market. For fleets that have moved to 30w oils, they seem to be going with 10w30. I have seen or read of several fleets moving to 30w, especially this year. Detroit is factory filling their DD13 and DD15 engines with 10w30. They are even recommending 50,000 mile oil changes on this oil. The 15w30 thing seems a little out of place for what the market seems to be moving toward. The 10w30 is getting used in engines from Detroit, Paccar, etc that are regularly pulling gross weights up to 80,000 lb, in the mountains to the flats, in Canada in the winter to the Rio Grande in the summer. Not sure how much more severe duty this 15w30 is going to fill a niche for.