I doubt many schools will care that a student took Spanish 3 at a CC or via UC Scout, etc., rather than the HS. Many students take core courses outside the HS for many reasons. The schools that might care are more likely to be highly selective schools, but even then, I’d need some data to believe it.
I wouldn’t count on Spanish 3 being less time consuming if taken outside his HS though.
Has your kid talked with their HS counselor to get their thoughts?