[fun in dirt]

On that Jeg's page you can click on the "For a complete list..".
It says the 15x8s have a -27mm backspacing (=1.06 inches) and the 15x10s have a 38mm backspacing (=1.5inches). So that all should mean the 15x8s should be about 3.94" & the 15x10s about 3.5" from the back edge of the wheel to the centers. Which all seems normal.
Good looking Blazer!