Thinking about Certification

I have researched a variety of films from the same Genre as my own, and I have decided on the Genre I am going to use. I have decided that I am going to certify my film "15", as I think that my film has intense themes in it (for example: violence, drug use, mental problems) with may not be understood by people aged below 15. My film does not contain strong nudity, sexual references or gorey violence and therefore my film cannot be certified 18. I have decided against 12A because I believe that the films in my film are too intense for young teenagers.