Re-igniting your passion for your work sound like a good project. Fifteen years is a long time so good for you for hanging in there so long.

I work in health care and I have had to do the same thing. Sometimes it is as simple as taking time to remember why I went into my field in the first place and what is still going well in my work. Other times I have done things like changed jobs within my field by moving to another department. I also went back to school and expanded my degree. If you don't want to go back to college, are there any certifications you could consider sitting for? Or maybe just attending a conference on something about your job that interests you would help. If you like to write, you could start a blog about your work - you just have to be cautions about the anonymity issue.

Best wishes. That you are taking the time and responsibility to look into this issue tells me you are probably good at what you do.