15 day itinerary - please review

Not a bad looking itinerary.
A couple of suggestions: on your drive down to Kilkenny consider a stop at the monastic site at Glendalough in the Wicklow mountains, especially if you can get an early start on your day in order to arrive before the tour buses (and crowds) start to roll in at 9:30 when the visitor center opens. The site itself is always open and having it all to yourselves is worth the effort.
Consider too driving at least the northern portion of the Ring of Kerry while you're in Dingle, to include the exquisite Gap Of Dunloe and the very pretty Skellig Ring Road near the village of Portmagee.
Near Dingle too is Inch Beach which was featured in the film "Ryan's Daughter", and a very cute little pub call the South Pole Inn which was originally established by Tom Crean - Second Officer on the ill-fated Shackleton polar expedition of 1914. The pub is essentially a little museum featuring photos and artifacts from his long and colorful career.

You might investigate the boat to Inishmore that includes a pass by the Cliffs of Moher - that way you avoid the traffic jam of buses at the top and extends your time doing other stuff.

If you're looking for an extra day, maybe add Clonakilty or Kenmare on the way to Dingle. That would allow a stop in Killarney NP with the shorter drive. Or add Westport, Clifden, or Donegal. There are a lot of choices of great spots all over Ireland. You can't go wrong.

Another thought is to spend two nights in Kilkenny, to give more time in Glendalough, and maybe reduce Kinsale to one night if you find other additions.

You could add a night in Athlone between Galway and Trim. It has a castle, an old pub and the nearby Clonmacnoise monastic settlement.

Thank you for your very helpful responses! A photo at the Gap of Dunloe was actually the inspiration for this trip, but I wasn't sure how/where to fit it in and forgot about it. I will drill down and look at each suggestion.