Not sure I buy the reasoning for no 15-40, fwiw.
May leave a film or buildup? That’s pretty laughable.
And too tight of tolerances? Again seems like bunk unless talking very cold weather.
My opinion is based on historical “requirements” and how they seem to vary so much brand to brand, year to year, engine to engine.
That and hydraulic lifters aren’t magical. I’ve run 15-40 in many Hyd lifter engines including a couple that “required” 0w40. 150k miles later it ran fine and didn’t burn any oil, leak, make noise or any lack of performance.
But am interested in a better explanation of the requirement as all I’ve found is very vague articles. As always Icbw.