I don't know about Phuket, but Jomtien immigration office told me to come back a week before my exemption expired as they were too busy with the 90 day reporting
If my flight isn't until after 15th day though, it shouldn't matter if I apply before then. It's not like I would be able to get on an earlier flight with the checks conducted by the airline
I'm kind of in the same situation. I'm currently at day 11 after the one dose J&J vaccine and I applied. Haven't heard back yet and am due to fly out on the 15th
Thanks, I hope so. It's the not knowing that's getting to me. I would rather get rejected early than hear nothing until the last moment. Enjoy your time in Thailand