15 years in, formal eduction shouldn't be a big deal. Assuming you made a deep positive impact on successful projects, you should have a deep network or connections and referrals to tap? If not, you need to answer that question.

Why are you "bluffing" through jobs when you should have a large tool-belt of experience? Just-in-time/on-the-job learning should be a positive, but it sounds like you need to improve your soft skills/be able to more effectively reposition/sell yourself.

Beyond a resume, which you've mentioned you're terrible at (learn to make a good one, there are plenty of resources, or get someone who is good at it to improve yours) you should probably also put together a CV/project portfolio. Is your LinkedIn up to date?

Also, while it sounds like your experience is mostly in IT support/systems integration, if you're looking for employability, just learn to code. iOS/Android if you're looking for immediate employability, some systems language, full-stack webdev for more general flexibility.

Participate in some open source projects, like others have mentioned, make sure you have a robust Github account. The only way to judge talent is by output, and having public repos and project participation speaks for itself and is a 100x better indicator than any degree or credential.

I wish you the best of luck, but you maybe getting feedback from former employees and coworkers to assess your strengths and weaknesses would be more effective than asking random people on the Internet?