LOL. It's your truck. I'm a diehard Amsoil user & fan. I've spent a small fortune on UOA with Amsoil and I'm a real believer in their products. I was "funning" with you. To be serious, you're the one who said your son is planning to go to 15K on this OCI. I wouldn't do that without having UOA for support. On Amsoil SS "extended oil change intervals" which I believe THEY define as "longer than manufacturer recommended," I would want an oil analysis somewhere ~12K just to be sure of yourself going to 15K. I don't know what your son's owner's manual recommends nor do I know what you're comfortable with....maybe run it as far as your son is comfortable doing and then UOA? I can tell you from experience that using their SS oils, they're not interested in initial UOA (to see if further use is OK) until you have 7500 miles on the sample. I can also tell you that Amsoil TBN is way higher than "lesser oils," so I'm not sure if I agree with "diluting it." TBN is 12.5, go the distance:
https://amsoilcontent.com/ams/lit/databulletins/g2880.pdf
I've run Amsoil SS oil changes far past 20K, but I run bypass filtration and I've got supporting UOA. The "cheaper" side of this discussion is that the UOA cost may be near the equivalent cost of the oil change itself? To which I would reply, you're setting precedent; trying to find the envelope of where is comfortable and practical. What is the oil capacity of said truck? Hope this helps you.