A decade-old Silverado can still be a useful work truck, tow rig, or daily driver, but condition and service history now matter more than trim badges or mileage alone. The 2015 Chevrolet Silverado 1500 sits in an interesting spot in the used-truck market. It belongs to the generation that brought a quieter cabin, direct-injected EcoTec3 engines, available 4G LTE connectivity, and a broad range of work and luxury trims. For 2015, Chevrolet also paired the…