For a 2015 model, the LEDs should last longer. For those dimmer or out, are those lights on a dimmer? It may be the dimmer is bad and you're getting fluctuation in the current from the dimmer. This happens with household LED dimmers.
If you have to change the lights, which is something I'm doing now to upgrade from the horrid cool white LEDs (I have a 2016 19' CB Flying Cloud), you may have to change out the entire fixture. Not all Airstreams are the same.
I have found that the LED recessed lights, the bulb cannot be changed, at least with 2016 and up. You have to change out the entire fixture. It's the prior year trailers with the Halogen bulb where the bulb can be switched out to the LED wafer bulb.
I love the site below for Airstream OEM parts and they have a large light section. My dealer wants $300/light for new fixtures. This site for OEM is $48/light. I can easily cut remove, cut the wire, splice and install myself.