Most people don't really pay any attention to laws anyway. They are just there to prevent someone say 20 having sex with someone about 15. Having said that, most 15 year olds, as long as they aren't drunk, would be able to know whether they are ready.
In South Australia it is 17, but most other parts of Australia it is 16. I wouldn't coonsider South Australia worthy of a whole different legal age. We aren't that special.
I think it should be 16 though, because 15 is year 10 over here...and that's next year or me!
I can't honestly say that I would consider it that early, but 16 seems reasonable to me.
It also depends on the partner, because I think the laws should be relaxed if you have been with your partner for a while, but you are still under the legal age. Say if you were 15, and had been with your partner since you were 13. I would think that those 2 people would be saying "Sure the law is there, but we have been together for a while, it isn't just a sex for the sake of it thing, you don't stay together for 2 years just so you can have sex."