A: It seems to me that your difficulty actually lies in the ease of your current position. There is no specific irritant—no workplace annoyance, no financial hardship, no long-held dream—spurring you to commit to any particular action. You may feel as though your current life offers no clues to what your calling is, but you certainly have a recent example of stretching outside your comfort zone: You studied and earned your degree. What drew you to study business management? Were there particular aspects of the field that intrigued you? Did any of the courses you took challenge you in the way that you want to be challenged? Within your coursework, did you find some assignments more interesting and rewarding than others? What did you get the biggest kick out of researching? Did you actually hate doing research but love helping fellow students or debating with your professors? The list of questions could go on, but I hope you see the point: You will find your passion by considering the particular details of what you have done and what you are doing, in the moment. The specific activities you love doing will lead you to the career you should pursue. It's easier to pursue a new career when you are passionate about what you're going to be doing.
One thing to consider about career transitions: Although you feel as though you've stagnated in your current role, that doesn't necessarily mean your current company is not the answer. If you can find a different role within your company that would play to the strengths you discover in yourself, it can sometimes be easier to take advantage of the connections you have and the trust you've built over those 15 years to gain some leeway as you move into a new field.