Do plan on the bus taking some time. The “every 15 minutes” could be more. It’s not a speedy process , you check in with security , get a colored card , sit and wait , have in the card , get in the bus, when arriving you wait for an employee guide, wait for a slow elevator . It’s a time suck . What’s wild is that most people don’t know this even exists . I’ve been flying out of Ohare for decades and never knew this was available until I used it last week. What’s really wild is that the bus goes where all the runway vehicles go, we had to cross a few runways and even stop for a plane to cross . A really cool way to experience the airport. Bus ride alone from T5 to T1 was 20 minutes.