It's all about responcablity...you will have lives depending on you for daily care. Are you up for it? Do your parents trust you to do it all in the pouring rain? Heat? Cold?
A few chickens are easier to care for than one dog.
Do you have a plan for housing?
Have you researched associated costs?
I think you should read, ask questions, read more--then put together an outline of what is involved and how you will handle it. Find out what your parents' concerns are and make sure they are addressed. Ensure that your behavior and chioces in the mean time are showing you can handle the responcablity.
Chickens are easier than many other pets or livestock. You would be improving the quality of the family's diet, becoming more self sufficaint, and eating as locally as posible which could reduce your carbon foot print (x2 if you supliment thier diet with freeranging, kitchen scraps, or produce from your garden).
Chickens eat bugs: although I have more flies now, have have signifigantly less tick and Japaness beatles.
They force you to be semi-active and outside everyday--if you lean towards being a couch potatoe this could be an arugement. There is a theriputic benefit to any animal...a plus in your turbulant teen years.