I studied the old AQA philosophy specification for both AS and A2 and found it very, very interesting. It should cover everything in RS and beyond. RE is mainly theological philosophy, and applications of certain ethics, philosophy covers the very nature of such ethics and more. We learnt about philosophy of mind, epistemology, ethics and philosophy of God. I would suggest doing philosophy. As for the college problem, you should decide whether or not the advantages of studying philosophy somewhere you don't like outweighs not studying it somewhere you do like.