Certification problems

My film is a 15 but is suppose to have a U genre. This is where anyone can see it. Some films have this option but I have opted out due to these following reasons. Whilst researching film trailers and certifications, I came across the widely popular Spiderman and it's certification problems. Spiderman had a U trailer which took the interest of many children, but when the was released, it became a 12. This caused an up roar among parents who had children very disappointed that they couldn't see this film. The 12A age rating then came out which was available for anyone to see as long as parents were with the kids. The film was then reviewed as being too violent for children that young and shouldn't of marketed the film at children in the 1st place. Due to this reason, I have decided to change my trailer into a 15 as well so I don't disappoint underage teenagers or children who want to see this film. This will impact the views of my film, but hopefully there will be no aggro with the certification. It is now advertised to only people who are able to watch my film. Due to my trailer being a 15, I can now leave the partial bit of nudity in the trailer and it being ok around the guidelines. I may still blur his bum out for humour, but at the moment, It can stay if I wish.