I wish I had a 15yr old girl living next door to me willing to babysit

I would definately take her up on it and depending on how long you are gone for I reckon between $10 - $15 an hour would be fair.

Maybe give her a trial run but when you are home.
Her been the main caregiver and you can do all those little jobs that never seem to get done with little people around (ie read a book with your feet up ) Then you can oversee her interaction and make sure you feel comfortable with her.

Good luck