Courses are probably worth a different amount of credits at each school. That being said don't go too crazy lolI seem to be counting 15 credits?
I have seen this done before by friends of mine (5 heavy courses +20ish hours a week of waitressing). They pulled off 3.8+ marks (probably like a 3.9), but it certainly did not look fun.
Is there a way to replace one of your science courses with a chill elective, and then taking the science course during a lighter semester?
I can't speak from personal experience as I have yet to have a semester like the one you described. This coming semester, I plan on working 20 hours a week, but my 5 courses aren't as tough as yours (or at least I hope they won't be hehe).