This system would see a more relaxed approach to teaching, because of the extra years available to gain GSCE's or O', A' levels. Kids could take their 1st exams around 11, class room tests for younger pupils, should be sufficient. There'd be fewer young people claiming benefits, and feeling worthless, more jobs available to over 18 year olds, perhaps even fewer teenage pregnancies. It could, even slow the rest of us down, because at the moment we begin running around like headless chickens from the time we start school, 'til the time we retire. All the stress related illnesses then catch up with us, so we don't enjoy our school days, our working lives or retirement. It's not some individuals who need to chillax, but society.
I think the school leaving age should be raised to 18. We are constantly being told how our life expectancy is increaseing, we therefore have more time than previous generations or populations. In some developing countries women can expect to live only into their forties, so of course 15 is a good age to become a mother, 30 to become a grandmother. Here in wealthy Europe, we live alot longer, so there's no rush. Let's be children, without responsibilities or stress for our first 18 years.