I took off a long time from cycling, got fat, lost all my muscle, heart strength, and lung capacity, and found that a two-percent grade is a serious "hill" to me now.

Also, winter riding is Very tough on my lungs (asthma since age 5 or so.) If you really think it is necessary, visit a doctor for some tests. (Don't mess around if you really think you have issues----when I finally broke down and sawe a doctor he scheduled emergency heart surgery. if I had ignored it a while longer ... there would be a lot fewer pompous, rambling posts on this forum.)

But ... if you feel that what you are experiencing is the product of 15 years on the couch-----and 15 years is a Long time as we age, not like when we were young and could recover from anything right away----well, keep at it. Don't try to do it all at once, pay really close attention to your body, expect to take longer to improve and to recover, and just go out and enjoy riding your bike.

I find my definition of "push" is a Lot different now. I still like to push myself a little---but the gain/recovery ratio is very different. I can push really hard but I might lose all the gains by the time I can get back on the bike safely. Now I "push" by going a tiny bit harder for a very short time, or by trying to go a little farther every now and then. I realize that the biggest gains won't be performance---the biggest gains will be just being able to ride around and enjoy it.

Improvement comes, but so slowly it is no longer worth waiting for. I get my thrills just pedaling around, and when I realize I am a little quicker or that last hill didn't hurt Quite so much as it used to ... great! But just being able to make it up that hill, struggling, wheezing, looking pathetic ... if I make it, I win, no matter how long it takes (if I have to walk---I still win.)

Congratulations for taking up the bike again.