15+ model year doesn't have air suspension at all. It's a mechanically adjusting system as Andy said.
The 3rd-gen has rear air suspension as an option, most of the Limiteds I see in my area have it. If it has air suspension it replaces the coil spring entirely, you won't see a coil at all underneath. Also, the air suspension option requires the 301A option group on the Limited, so if you see a Limited without a sunroof, it doesn't have air suspension either. If you have the VIN you can look it up in
Ford ETIS and it will show you all the options it was built with.