PPE is better if you want a finance job due to the Econ element but tbh if you have any degree from Oxbridge you will have good job opportunities. Also for PPE at other top unis (LSE and UCL) you are required to have an A* in maths A-Level, let alone GCSE. Economics may seem like a drag if you don't even like maths to a GCSE level.
You are still in year 10 so you could still probably achieve a 8 or 9 in maths, predicted grades are not that accurate before y11.
So overall, job opportunities will be great for anything you do at Oxbridge so pick the course you like more! (Btw Cambridge offers HSPS or Land Economy and Oxford offers PPE)