I'd probably accept that brakes designed for a modern truck with a 15,000 GVW would probably be good enough for something like my 16,000 GVW 6400.
My K3500 is not a dually, but you knew that from the GVW. I thought about a dually, but wanted to drive the truck everyday and an extended cab pickup with an eight-foot bed can already present parking challenges. Make it more than a foot wider and it gets worse, as I'm sure you already know. I pull a car trailer with it that has never challenged the truck, so I feel it was the right choice for me.
One of my projects is creating a dually pickup with a style-side bed based on a '53 GMC panel and parts of a Chevy 1-ton panel. The frame I plan to put it on was marked with an 8800 GVW and my brakes are coming from the 12,000 GVW P30.
