My experience has been that 15 minutes will get them to more or less 50%, but they get slow to charge after that and it can take better than an hour to fully charge them.

but yes, you can put them back int he case for 15 minutes every couple hours and not really worry about it. That said, I have tinnitus from years of working in a noisy datacenter type environment, and I'm very, very sensitive to being in environments now with loud noise or even moderate droning sounds like you get in-flight, and while I love my Airpods Pro and take them everywhere, in-flight I still rely on the Bose QC-20i which will go for a full 15 hour flight on a single charge.

For shorter flights, though, particularly domestics, I do use my airpods a lot.