What Makes a 15 Certified Film?

I researched into what classifies a 15 film using the website; bbfc.co.uk.

A 15 certificate film means that no-one under the age of 15 is allowed to view it, rent or buy the film. Issues such as drugs and sex are accepted, however they are not permitted to be shown in detail or to encourage. Aggressive and strong language may be used throughout the film, but not to a high extent where the strongest language is repeated purposefully. Violence and horror are allowed to be shown, as long as the film does not focus on the pain or torture of the character involved for too long.

The horror opening my group will be producing is aimed to be for a 15 certified film. This means that my group will have to stay to the boundaries of the certificate guidelines at all times whilst filming.