The tire interference in more times than not is not on the fender lips but on the drain tubes from the cowl.
The 7" wheels will move the tire out further away and provide more clearance there than the 8" wheels will.
I don't have any interference anywhere on my '73, spacers removed, 225-50-15 P7's, 8" Campi's with no spacers.
I don't see where you should have any issue with the 215-60-15 tire on either wheel.
George is right though. The 7" moves it further away from the drain tubes.
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