In an interview with Bloomberg, Apple retail chief Ron Johnson said the company expects the in-store setup process for the iPhone 3G to take around 15 minutes, including credit check and activation. “Our expectation is that in 10 to 15 minutes, you’ll be set up and ready to go,” said Johnson, adding that each of Apple’s more than 185 retail stores in the U.S. are aiming to handle about 100 customers an hour. Speaking about…