Probably not as important at your tender age to do it in a short space of time as your learning curve and ability to retain information is far superior to someone like me of more advanced years.
I am doing mine at the rate of 3 or so lessons a week so i dont spend too much time covering old ground each lesson and it is being financed from a savings scheme as i certainly couldnt do it at that rate on my wage.
Its whatever you feel comfortable with both in financial and learning terms.
Everyone of us is different so if it feels right for you, then it is right, thats how i see it.