Not sure about venting it horizontally, that’s not code here but may be there for a simple fan vent. But for range hood vents, etc, they need to be vented vertically through the roof.
I would suggest you get somebody who is certified for venting. Just the fact you asked about venting a toilet through a 1.5″ sleeve is scary. And I would’nt terminate the bath fan vent in an attic unless you want alot of mold and mildew up there.