there is an absolute shxtload on here asking the very same here use the search above .
That said Im bored ,
If you want to be a pilot then forget extra curricular your first priority should be learning to fly , you are old enough (if you have the funds avail) because obviously you can have all the extra curricular you want if you cant fly then there is an obvious penalty there.
So in a nutshell start learning , join the ATC aim for a flying scholarship , get your foot in the door that way , look to the forces as an option they are possibly one of the only organisations in the world currently recruiting , not that that matters being as you're 15 , but it all helps when the time comes.
The search function above will answer virtually every question you can ask
good luck