When I got my Merlin I was having a near hourly debate between Merlin (which is now being built again by RedFeather), Kee15, Peregrine, and Northwind Solo - all DY boats with a shared heritage. I do love the Merlin, but I have been surprised at how much more stable the Keewaydin feels in comparison. I like playful boats, but still - it is nice to have that stability at the end of a long paddling day. What is odd to me is that the specs are not much different between the two - the Kee is 1/2" wider at max width, 1/2" deeper amidship, and actually has a narrower gunwale width. Not that this would impact stability per se, but the Kee has 1/2" less rocker both in the bow and stern. Perhaps the contributing factor is the waterline width? the Kee is listed at 27" while the Merlin is 25.5"; the Merlin II certainly does feel quite a bit quicker to heel as a result.
Regardless, would love to hear more about your experience paddling both - I sort of feel like the Merlin is optimized for kneeling while the Kee15 can be paddled sitting or kneeling (of course the Merlin can as well, but many feel it's a bit "tippy" when seated, which of course would be the case if you have a kneeling depth seat in a shallow boat).