Could you help me with two questions about the sentence below?

I never got the feeling they felt as driven to actually do it as I had since adolescence.

I think the main clause is "I never got the feeling".

Q1: I'm not sure what kind of clause "they felt" is a part of. Is it "I never got the feeling which they felt ..." or "I never got the feeling that they felt driven to do it ..."? If it is the latter, then it is a nominal clause, can "that" be deleted in that case?

Q2: Is "I had since adolescence" reduced from "I had felt since adolescence"?