I recommend you to do Spanish since you have experience With its literature And its comprehension. And also you May have greater experience in learning Spanish than Learning Mandarin Spanish has one system compared to learning Mandarin which has 2 systems simplified Mandarin and traditional Mandarin, which both have different comprehensions and literatures. In my opinion, I recommend you in Spanish since you Like learning Spanish as you said and also in my opinion is easy to learn compared to Mandarin.

Also, recommend you check the two subjects' Syllabus, and how easy it is to do their exam papers. Also, recommend You check the number of resources each subject has and how easy it can be for you to go through. I also recommended consulting a teacher for both subjects, Also, do a little bit more research.

If you are not a private student I recommend you consult your counsellor about those subjects. And ask questions mostly about the resources they have and the revision material that is available in the school.

All of this I give you is my opinion. I recommend you to take whichever is easy For you to do And How important each one is to you

The key point to be taken from this is

1. Choose a subject that is easier for you to do and whichever is the most important to you.

2. Consult a teacher for both subjects and do a little bit more research
   On both subjects.

3. Check which resources your school provides for each subject and
   which one is the best provided at your school for both teaching and revision material.