I'm so sorry about your beloved kitty, and I agree with Beatrice on this. Tell your XH what you've decided.
Long ago, I went to school for, and then worked as a Vet Tech. I can tell you that a cat that is 15 years old has reached very old age and attests to the excellent care you have given her.
As far as surgery goes, at her advanced age she probably wouldn't survive it, and you're correct that you'd only be trying to delay the inevitable.
It takes a strong, loving, compassionate person to put their pet's pain to an end knowing how much you'll hurt and miss them.
I had a very old mare, and in the spring before H left 2 years ago, I talked to him about euthanizing her because her quality of life was rapidly declining. At the time he agreed with me because it started to become difficult for her to get around as arthritis had severely affected her joints.
About a month and a half after he left I had my Vet come and humanely put her to sleep as I wouldn't put her through another winter. Our son told his Dad about it after the fact, and I was very surprised at how emotional S said my H had become about it.
I'm telling this story just because I wished I had informed H that the time had come because he may have wanted to come to say goodbye, and I didn't give him that chance.
