WOW!! I would hate to be his English teacher.
Yeah you can perform at malls and on the streets when you are 15 but I doubt you can live off of the money you make. You're 15, you most likely live at home with parents. This means you don't have to pay: rent, food, electricity, car bills (if you have one), phone bills, mortgage payments (if you have a house, then rent is out of the picture), heating and water bills, hmm, that seems like thousands of dollars worth of money to spend just to stay alive and have shelter. And it seems to me that you said you make enough money to buy tricks here, well, hate to say it buddy but, that isn't enough money to be considered a professional or to live on your own. Study harder, and go to school and you will be able to busk apart from your regular job which will let you live.
The bottom line is that you can perform on the streets when you are 15, if you are good enough. But, you will not make enough money to live off of it, and you will not be taken as seriously as someone who is 18+ and actually looks like an adult, and you will make less money than the same person.
Don't take this as a dampening of spirits, go ahead and perform, get better, then when you are 18 or older, you can make much more money off of it. Just my opinion on it.
Oh and by the way: This is my 200th post!!!!