I think the 235 tire is too narrow for an 8" wide wheel. Especially a 75 series on a 15".
However, check the tire manufacturer web site for wheel recommendations for the tire you are purchasing. I'd suggest considering a 7.5" wide wheel (max) for a 235 tire.
To maintain an appearance similar to factory, I'd get around 5" backspace. A 4.5" backspace will poke a lot, 5.5" backspace is too inward.
This link will help you read offset values for different wheel widths to achieve the backspace of your choice.
For reference, your Z85 wheel should be 6.5" wide with +41mm offset. The width is printed on the manufacturer sticker on the driver door jamb near the latch. The offset value is stamped on the inside of the wheel (removal from the truck is necessary to see).
So remember, closer to 4" makes it stick out, closer to 6" pulls it in (relative to stock).