I have the original Rocna 10 kg on our 2017 C-28. Required a bigger Kingston KR-1015 bow roller to get clearance from the anchor’s sharp tip and the hull. Plenty of clearance between anchor and hull now. But the bigger bow roller means less clearance between the bow roller+anchor and the top of winch mast on the EZ Loader trailer. The solution for me is to move the anchor onto the deck of the bow when launching and retrieving. That works, just an extra couple of steps involved.
I’m not sure how I would make a Rocna 15 fit everything. We have not had any issues with the Rocna 10 kg at anchor.
PS: I have serious doubts about the new Rocna II or the Vulcan anchors fitting on the C-28 due to the limited vertical space in the bow roller tunnel. The arched spine of those anchors is just too tall.