Ths issue is not about study permit. Some bachelor programs are 3 years instead of 4 years. You should inquire from the university/College you want to apply and you can be accepted based on your 15 years of education. If you get acceptance letter then you can apply for study permit.
Its not mandatory and is a requirement only for some courses especially if you are planning to do masters. A 3 year degree or a diploma is enough for most of the PG diploma courses. Again it depends on which course you intend to pursue.
If you've been advised and it looks good deal for you, then take it! People here advise based on their experiences. People got 15 years education and got study permit to pursue 2 years PGD. It's all up to you. GOOD LUCK!