[rickst29]

With odd numbers of bolts, there are several ways. With 6 bolts, however, it is generally agreed that the correct method is measuring between the centers of directly opposite bolt holes.

My wheels have 5.50 inches (= 139.7 mm) between centers. I'm quite confident that an Internet order of such wheels, 15*6" with minimal offset, will be fine. If you are also buying new ordering lug nuts (and it is recommended, by many sellers of tires, to always replace the lug nuts when you install new wheels): the size I have measured on my own is 1/2", 20 Threads per Inch. (NOT 12mm, NOT 14mm). But measure your own, this may have changed in more recent years.