CK-4 oils in an older 5.9 Cummins engine

I've been using Rotella T6 5W40 oil for years in my '02 Dodge Ram with no problems. As I'm approaching 200K miles on the rig I recently switched over to Delo 400 XLE 15W-40 thinking the heavier oil would do a better job on an older engine. The Delo seems to be doing fine, is way cheaper and I have no gripes with it.
Foolishly I started looking over the specs (you can't stop once you start down that rabbit hole) of these newer CK-4 oils and was a little shocked to see the Zinc/Phosphorus levels down under 700 to 800ppm. Seems like the older CH4 and CI4 oils had way more ZDDP than this new double. Those AW additives were considered good for a flat tappet engine. Just wondering if I should look for another oil, stick with the Delo, do more frequent oil changes or just stop looking at the specs?
The 15w-40 isn't heavier per se. I don't have time to look up the specs, but it'll probably be similar in viscosity to the 5w-40 when the engine is at operating temperature. I would want the 5w-40 (if money wasn't a concern) for cold starts in an Idaho winter.

A good indicator for phosphorus content is whether and how the oil is dual-rated. If it has an SP rating, it will have to stick with the 800ppm limit.

AFAIK, Rotella T6 5w-40 CK-4 has around 1000ppm of phosphorous, 1200ppm zinc. There's a VOA floating around on this board somewhere comparing CK-4 and CJ-4 versions.

Edit: found it -->
The American West
I don't get what the big deal is with looking at specs. That is how some of us know what goes into our crankcase. There are a few here getting snarky about this concern with numbers in oil. Who cares who approves it???? This is sorta the "if so and so jumped off of a bridge, would you" mentality. I want to know for myself. It's my time and money. Seems the American way to self reliance....and so on. Why is there a problem with this? Isn't this an oil forum? Isn't the point of this forum to be INFORMED??? Seems like it to me....