Now I know what most people are thinking, kids are too immature, or ignorant to vote. But for my friends and I, we have known more about voting situations then our parents the past 2 times. Now I have a group of very intelligent friends, and believe me I know that not all 14 and 15 year old are like that. But trust me on this the teenagers who don't want to spend the time to learn about the current political situation truly don't care enough to vote or even "waist there time" thinking about it. I have only met a handful of teenagers who keep up on current events,and those are the only ones who would vote before at least 18.
15 year old's are not mature enough. The large majority still live at home and go to school. They may have adult bodies, but their minds are still those of children who have to be protected. By 18 they have become much more independent and are able to make their own way in the world. Their political views are likely to be more thoughtful compared to 16 year olds, who may just copy their parents opinions or adopt silly ideas for the sake of rebellion.
It would be dangerous to give young people the vote. They might use it in foolish ways. For example they might vote for celebrities or make their decision on which party had the best image. They might put extremists into power or vote without thinking on single issues (e.g. making drugs legal, free university places, cheap beer!).
Just because 15 year olds have the right to do some things, it doesn’t mean that they should use them. If all 16 year olds left home at 15 and started families it would be considered a disaster. And not all rights are given at 15 - most countries have a higher age for important things such as drinking alcohol, serving on a jury, joining the military, etc. It makes sense for different rights to be gained at different times as young people mature and get used to more responsibility. Because voting is so important, it should be one of the last rights to be gained.