What do you plan to do later in life? If you want to do anything related to drama and theatre as a career, then drama GCSE is the way to go. If not, it wouldn't really be that useful anyways. Of course, if you love the subject, the you should do it but if you are having doubts, then it may be best to reconsider.
Of course doing 2 languages is good! If you are able to handle the workload, then Spanish would probably be what I would take. The more languages you know, the better. Even if you become an intermediate speaker in that language, it would be much easier to advance later on if you choose to do so. Learning more languages can open more job opportunities and being bilingual or multilingual is what employers typically favour. The more languages, the better. You would be able to communicate to more people around the world. Although GCSEs aren't really recognised qualifications internationally, this is still a good way to start learning a language. Maybe switching to Spanish is what's right for you.
I am, yet again, asking, what career do you have in mind, and is it related to drama? Personally, I am not preparing for Drama or Spanish GCSEs but I have a friend that is taking Spanish GCSEs and she seems to enjoy it a lot. Hope this helps!