ahh....I see you are 15. My advice to you (from what I have learnt reading many post on this forum) is that you use the next 3 years to do as much aviation and leadership things you can, as you can't join the RAAF untill you are 18. This will show them that you are passionate about aviation and have leadership qualities. Then apply for pilot/ACO as a ADFA candidate, as it is very hard to get in at 18 yrs of age through direct entry. And remember you need maths and physics in your HSC to be a good looking candidate.
Hope this helps and good luck.