What is 15b AIT refresher like for prior service?

I was a 15B for 9 years before I switched to a 19k. I submitted a 4187 to go back to a 15B. So far everything looks good, the aviation branch said good to go, armored will let me go, now we're waiting on HRC to sign off or deny. I'm curious how long the refresher would be if they require me to do one? Second, I did the 4187 I would not be able to go back to 15B if I waited for my window to open in December, would I still be able to get duty station of choice when I re-up since I would be re-classing? Retention here is a joke and not offering any insight into how the process would work. Thank you for any insight.