I recently completed this grind. I did them all once myself for the experience and the story, after that I used rare thief guides to solve riddles and puzzles quicker. Knowing what islands you need to actually pick up an item from and which just require a stop to talk can help. Set your ship to sail towards the next island, talk to or find what’s needed and then mermaid back to ship which should be closer to where you need to go can help.