My 17 year old son has had asthma since toddler-hood. His pediatrician avoided doing anything that would create a preexisting condition status on our insurance for years. He had his first and only PFT when he was 15.
His asthma is fairly mild and mainly exercise induced. He has had some pretty scary cat episodes but those are easy to avoid.
He did gymnastics from 2 1/2 to 11 and the chalk was pretty rough on him. He is very tall so he switched to figure skating and the chemicals they use to chill the ice were worse than the chalk. He was finally sent to the Pulmonologist.
Now he is 6'4" and he only skates for fun. He rows with his big brother. The ERG training has done wonders for him.

It would seem to me that a yearly test is either excessive or your doctor has not done a very good job communicating why your specific condition warrants the yearly test. You may want to question them about it before they set up the next test.