I just got braces not too long ago, halfway through Year 11, so they will be taken off in Year 13, which is before university, and before the interviews too hopefully, so I am not in the same position as you.
But, it depends how you feel about your teeth. I thought mine weren't terrible, and my mum didn't want me getting them because my teeth aren't too bad. Even the dentist and the orthodontist said that they weren't 'necessary' but will make an improvement, so I said yes.
Don't worry too much about lifestyle changes, because your diet will change, but for the better, with less fizzy drinks, and bad foods, etc. And brushing isn't a problem (for my teeth anyway).
So, I would go for it. They're free! Plus, you will probably regret not having them in later life.