Certificate Research

My film will most likely be a 15 but by looking at films similar to mine I can see what the most common certificate is:
American Beauty-18
Hard Candy-18
Trainspotting-18
Requiem for a Dream-18

From looking at what makes an 18 and 15 I can see my film will actually be an 18 unlike I thought. This is due to the strong language that would be in my film(not the beginning however). There will also be used of drugs and abuse in the beginning that is shown.