Can you adjust the time temperature to cook two items at same time if the bread calls for 15 min at 375 degrees and chicken calls for 30 min at 350 degrees?

Not really a great idea. But if you're going to do it anyway, cook the chicken at a lower temperature for longer, then crank it up and good the bread as directed. That way, the chicken will be cooked through, and the bread will come out right.

The bread is more sensitive, so you should bake it as directed.