I'd have 15" overhang on both sides--seating on two sides is more conducive to conversation and interaction, and your plan seems to have plenty of room for stools on the right side.
Also, even though this thread is about the island, if you could label your appliances on the plan, the pros here (one of which I am not) could check over the functional flow and make suggestions, if necessary. I don't see a water source in the island, or much prep space beside the cooktop. It looks as if the DW is to the right of the sink (in the plan, but sitting in the family room currently ;), but I think it might work better on the left side.
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