I made a post during the playtest at some point about flying speeds, but I can't find it now.
The slowest non-hovering fly speed of any actual bird is 5 mph (during courtship displays) which is a little over 7 feet per second. This is a reasonable baseline for non-magical flight.
As rounds are 6 seconds long, that translates to 45 feet per round.
A fly speed of 15 feet is ridiculously slow. Yes the 3 action system means you can spend up to 3 actions flying (and reach that 45 foot 5 mph speed), but it means you can do literally nothing else in order to be as fast as American woodcock when it's trying to impress a mate with its ability to not fall out of the air.
If you only spend 1 action on moving you are just barely out-pacing a mosquito, the slowest flying insect, at 1.5 mph.