Hi Memsmum,
IT system is similar to the UK in a way: primary (compulsory) school starts at 6, then you have middle school til 15, and that's when compulsory stops, with the equivalent of GCSEs. after that there are various highschools, for more academic ones ("licei") it's 5 years, end of which is the Maturita' (which gives you a diploma), eqivalent of A' levels, but there more comparable to the french bac a laureat (in some, like the language school I attended you also need to prepare a mini thesis too). otherwise there are the technical schools (i.e. to do with electronics/mechanics/it for engineers etc), which can be split in 2 + 3 or 3 + 2 years (second part being specialisation), always ending with the Maturita'. then you also have more "professional" schools, like secretarial, hospitality etc. A' levels/NVQs equivalent, like colleges here. basically in the UK you take the different A' levels/NVQs, in italy you have specific schools aimed at the different "orientations".
so yes, AFAIK he could leave at 15 (there were talks similar to here to raise the age limit, but our "resident" edu expert Franca's just gone on hols, otherwise she'd fill you in better) but he might be convinced in giving the chance to one of the professional schools hopefully (my brother hated school until he started the technical electroteck school, he did the whole 5 years, came out with flying colours and first job he got he got promoted to supervisor within weeks)
hope this helps