When I was 15, I dated a 19 year old.
I was in 10th grade and he was a senior. I was young for my grade and he was old for his. We went to different schools and bonded over the fact that we were both super into skiing and in the music scene.
My mom had no idea that he was 19... I just said he was a senior at the neighboring school and my mom was fine with it. Since I was younger, most of my friends had their licenses and it was super easy to get around. So getting dropped off at places was easy.
It entirely depend on the maturity of the individuals. Not that much changes between 14 and 15. Perhaps she went through puberty at 11. Maybe she is hyper intelligent and has traveled a ton. Perhaps in her own family, her father is 15 years older than her mother and they aren't bothered by the age difference but rather just want her to stay focused while in high school.
It's funny, the focus we put on age in this society. It takes about 2 years to get used to your body after puberty. As long as the decisions you are making are yours, you are mentally healthy, and you are mature enough to be in the relationship, what's the big deal?
Of course, many females aren't mature enough to handle it, but who are you to decide for them? Sometimes it takes a failed, awkward relationship to figure it out. It doesn't mean they had sex or laws were broken, just that they required the experience to realize it wasn't right for them.