In my opinion, a "child" shouldn't get to decide if they want to spend more or less time with a particular parent. The parents should determine what is in the best interest of the child. If either parent is manipulative or abusive, alternate arrangements may need to be made meaning supervised visits.
Children generally will choose the "fun" parent, the one that disciplines the least or lets them have whatever they want, video games, unrestricted computer access, staying up late, etc.
Generally I would probably let a 15 year old have more input into who they would like to spend time with while managing time spent between school work, friends, and social activities and obligations. I say 15 because this is around the time in our family we begin the great push towards independence and out of our house (preparing them for college and grown up life).
I hope this helps.