Some school systems make students explore major subjects beginning at fifteen, whereas others expect students to learn a broad range of subjects. I totally agree that schools should focus on specific subjects.
Studying major subjects as much earlier as possible can provide a lot of benefits for future careers. At the age of fifteen children already can decide which field of work they are going to, so it would be more effective to focus on specific subjects. For example, medicine, this field requires a high level of knowledge in biology and chemistry. Studying these two subjects more often than other unnecessary courses increases the chance of fully immersing in the field. Also it gives schoolchildren plenty of opportunities to have experience and practice the obligations during work, because for medical science it is important to have a lot of competence.
Minor subjects such as mathematics, history and geography are equally important for students. I would even say that is the base of a school education program which prepares children for versatility at any work. So this gained underlying knowledge may help to solve a question or problem appearing at any workplace, which will show that your wide range of knowledge and the ability to use your own soft skills. However, I would prefer learning something bigger than these basic areas, because I consider it as a waste of time and energy at this young age.
In conclusion, schooling systems should be directed on teenagers learning main areas of study rather than less important topics for specific fields. Thus, children have more prospects to be a professional, because certainty and determination are the key of any sphere.