Target Audience

I have been doing some research into a common thriller films target audience.
I have come to realise that the most successful and atmopsheric thriller films are rated 15 as there is availability to expand upon your ideas within your film. However, a fifteen will cut off our availability to a younger audience, so I believe that the opening sequence we have been creating should be certified as a 12A, as we can reach a wider audience, but there is a warning that children under twelve will need to be accompanied by a parent to watch the opening. Leaving us with a wider audience, without having any negative feedback from families.