Your description of Mollie reminds me of my old boy Josh
in his last few years.
Josh lived until almost 17. I lost him in 2004, which is quite a long time ago, so I don't remember exactly when things changed over the years for him, but I know that by Mollie's age he was deaf, had lots of warts and a few lumps that were fatty and harmless. I didn't have needle biopsies done on the lumps because the vet was pretty sure they were harmless and none of them was large or affected his movement or quality of life. Josh also had mild heart failure and a low grade heart murmur, both diagnosed between about 10 and 13 years, and both well controlled by daily medication.
At about 13, maybe 14, Josh had an anaesthetic for a much needed dental and to have a couple of troublesome warts removed. One was on the top of his head and he kept knocking it. The other was on his chest and he kept scratching it and it was always infected. I was really worried, but even back then anaesthesia was pretty sophisticated and he had the latest and newest one and recovered very well, if a bit slowly. He also started losing his sight to cataracts at around that time, but he adjusted well, probably helped by being slow and ploddy and therefore less likely to bump into things.
When he was 15 I thought I was going to lose him to a nasty liver infection. He was very ill for a couple of days but then rallied and started to pick up. It was around that time that I went through a phase of constantly worrying about him. Every morning I'd come downstairs worrying that he might not have come through the night. If he had the slightest off day, being fussy about his food, or more sleepy than usual, I'd fear the worst. I'm guessing that you're going through something similar at the moment
and I think that's perfectly normal. We look at them and wonder how did old age creep up on them
It was taking a huge toll on me at the time. Josh was my only companion because my husband works abroad on long term contracts, so I'm on my own most of the time, and I was just constantly worrying about him and not enjoying him. Then I decided I needed to start thinking differently and start looking at every day with Josh as something to celebrate. So even though his walks were slow and limited to about 10 minutes off lead pottering about and sniffing in the New Forest I could see that he still enjoyed them. Even though he slept most of the time I knew he was still contented when awake, enjoying a cuddle and a gentle groom (or any attention really), a bit fussy over his food but still mostly enjoying it, loving a patch of sunshine in the garden or sun streaming through a window indoors. I was confident that although what he could do was limited he was still enjoying those things.
I hope this helps? Mollie isn't worrying, she's just getting on with life, and as long as you think that she has a happy and pain free life, even if it's definitely life in the slow lane, then please try to stop worrying so much and focus on enjoying your lovely girl
and hopefully some lovely times still to come