Changing careers at 15 years into a job, is it realistic? - what worked for you?

After 15 years as an accounts payable clerk I am thinking about moving into a different field. Any experience at all would help. I have a little time and a small budget for training. Has anyone made a similar move?

Thanks for writing this out. I went through something close to it last year, and it got easier once I kept a simple log of every call and form.

Try a small project in the new field before committing. It told me a lot about whether I would enjoy it.