Is my itinerary feasible?

Personally, I would do either The South of Ireland or the North. With the above itinerary, you will be in a car driving a lot and will miss seeing some of the cities/towns that you are sleeping in. We did 14 days last year and stuck to the south. We even skipped some of our plan stops ( Cashel for example) to make sure that we had time to stop, walk the small quaint towns, do picnics on the beach and get to meet the locals. We all agreed that the best part of Ireland were the Irish and we got to meet so many while just hanging out in towns, pubs, at the beach etc.

For example, your day 5 is crazy packed to me. It will take you 1.5 hours or so to drive from Kilkenny to the rock ( add 50% to the posted drive times to be safe) Most people take 2 hours at the Rock. From the Rock to Blarney will take you 1:45 minutes. We spent 2.5 hours at Blarney as the grounds were beautiful. Somewhere in there, you have to have lunch. At this point in the day, it is around 3 or 4 in the afternoon. Blarney to Kenmore will take 2 hours without stopping anywhere to visit. It is now dinner time and you have spent 5.5 hours in the car in one day and have not visited Kenmare.

Just my 0.02$

I agree with what Sharon said, too much driving. Day 5 also caught my attention as just too much, I think day 10 might also be too much. You are also passing by a lot of things to see and do in the Killarney area. I also think you should cut out the north on this trip and add the days to the Killarney and Galway areas. These are both great towns to spend a few nights in, though Killarney gets a bad rap for being touristy you will find both good food and good music along with the national park and Gap of Dunloe etc. You aren't spending any time in Galway (my favourite town), but it is a great base for touring from if you want to see the Cliffs of Moher, Burren, Connemara, Aran Islands. Also great for music and shopping. Slow down, and travel like you are going to return, it will be a much better trip.

Your day 5 is long and day 14 is as well. We did the whole island Dublin to Dublin in 15 days and went fast of course but saw what we wanted and had a great time. I think your pace works but you might want to stay between the Antrim Coast and Belfast rather than Portrush on day 13. Not really sure where to add the extra day. I would probably add a stop on day 5 or day 12. Are lodging reservations made?
We weren't lucky enough to visit Skellig Michael because tours weren't running. Have a great time.

I hope to make reservations within the next week or two, I have adjusted my plan as follows, seeing mostly same sights. I decided to take out the ring of kerry drive and The Skellig Michael to allow for another day. I really would rather drive and see Northern Ireland also so Im trying to fit it in and this is where i am as of now I also still have a blank slot day available to play with where it fits best. So i am thinking of putting it in the Day 5 place(or possibly dropping Blarney Castle and using elsewhere) Suggestions welcome. Also this new plan utilizes Galway as a "HUB" type setup to reduce driving and night stay switches.

Day 1 half day (Fly in)

Day 2 Dublin, (Sleep in Dublin)

Day 3 Dublin, (Sleep in Dublin)

Day 4 Rent car, Drive to Kilkenny (sleep in Kilkenny)

Day 5 Drive to Kenmare

Day 6 Kenmare,Drive to Dingle (sleep in Dingle)

Day 7 Dingle (sleep in Dingle)

Day 8 Drive to County Clare, Galway (Sleep in Galway)

Day 9 Conemara & County Mayo (sleep in Galway)

Day 10 ___________________ possibly a third night in Galway

Day 11 Drive to Northern Ireland (Sleep in Portrush)

Day 12 Explore Antrim Coast (Sleep in Portrush)

Day 13 Drive to Belfast (Sleep in Belfast)

Day 14 Belfast, Drive to Trim (sleep in Trim)

Day 15 Trim (sleep in Trim)

Day 16 Return Car Fly home from Dublin

Also would switching Kenmare for Cork be a good alternative to helping day 5.

I would consider adding the night to either Dublin or Galway. You only have a day an a half in Dublin which may not seem like enough once you get there. The same goes for Galway, if you had another day you may decide to do a day trip out to Inishmore, or tour the Burren area and Kylemore Abbey. Also, great music at the Crane Pub in Galway.