I've been working in the 'web industry' for about seven years. It's not your fifteen, but it has been enough for me to spot a few trends. And I have to break you some bad news - from where I'm sitting, the age of the web generalist - the mobile worker who knew a bit about UX, a bit about SEO, a bit about branding, and just enough technical knowledge to make the whole thing fly - that era is ending, at least for the near future. People are hiring dedicated designers, dedicated front end devs, dedicated back end devs. Even from the technical side, I see more and more specialization as the tech becomes too big and too deep for anyone to call themselves 'full stack' any more.
What can you do? Well, UX and design is a healthy field. Qualitative research, product thinking and graphic design are a great marriage. But if you're more practically minded, working as a business/systems analyst or product manager could work well. You could become a front end developer if you love the technology, though right now the JS world is experiencing serious churn in tools and approaches.
Let us address your age. You worry that employers will overlook older workers. I would like to think that's not the case, but I expect ageism is persistent. But consider - your age is really an asset. You have seen many organizations. You know exactly what is deliverable. You have delivered successfully for fifteen years. And age will give you gravity, particularly in a more management-facing job like business analysis. I would much rather stare down a hostile sales director as a fifty-four year old than as the twenty-nine year old I am. Remember that there can be advantages to certain stereotypes - enjoy them.