Yes, they are 5 on 5. Many full sized GM cars in the 50s used 5 on 5 x 15" and some Chev one ton 5 lug trucks/vans from the 70s-80s are the same. The lunch guy is correct but offhand I can't recall which cars, I think Buick, Cad, & Pontiac but not sure. I know I have a set of 6x15, 5 on 5 from a 80s Chev one ton van that I used when I first changed from wire wheels.
Dave