It is a hard combination of HL subjects, but if you want to do aerospace engineering, you should definitely do Maths and Physics HL. If you had to change HLs, it would be "better" to drop Chemistry and do Economics instead... But that would be pointless. You want to prepare yourself for engineering, so you would benefit from doing Maths, Physics and Chemistry at HL. Economics will not give you any benefits. Yes, it will be tough with those HLs, but if you like the subjects and are good at them, you should be fine if you put in the work. If you hate economics, maybe you shouldn't do it at all; otherwise, keep it at SL so you enjoy your IB more.