What certificate would be appropriate?

I have made the decision that the correct certificate for the film is 15. I know that although it is not obvious what our film is about, as we are only showing the opening of it if we was to hypothetically film the rest of it there would certainly be content which wasn't appropriate for children. I did consider making the film a 12, however I sided against it as at that age some children are a lot more mature and others who aren't might find the content somewhat scary. The film probably wouldn't end with the mother getting her baby back, and for an immature 12 year old to see something which isn't HAPPILY EVER AFTER might prove to be all too much.