15 days in September & going around in circles trying to plan!

I’m not an expert on using public transportation in Spain, but it makes no sense to go from Sevilla to Granada only to backtrack to Córdoba.

Excellent point jaimeelsabio, thank you! I'll update my original post now :)

Hi, Sounds like a pretty good itinerary, but did wonder about 5 nights in Sevilla with only 2 in Granada. Perhaps that's where you're planning some day trips? I biked Andalucia while in college, loved loved Cordoba, Granada IMO needs more time for the gardens and the Alhambra, which I understand now needs to be booked ahead, (I would check that soon) and Sevilla is nice but I would have said my 3rd favorite of the 3. Good luck!

I think Cordoba is the hub of rail lines going to Seville, Madrid, and Granada, so you could visit Cordoba first, second, or third if using the train. I don't see any problem with the itinerary except that it doesn't include "getting off the beaten track & exploring nature and small towns." Without a car that would be hard to do.

You have enough time in Seville to do a day trip to Jerez or Cadiz or Arcos de la Frontera, and you have enough time in Barcelona to do some day trips along the coast or up to Montserrat. I think you're wise to base yourselves for awhile in both cities rather than charging from place to place every 2-3 days. Unfortunately that shortchanges Madrid, but the flight logistics seem to be your main reason for going there. If you land early in the day, you might see about going straight to Seville, by train or air, that same day. Or maybe you want to get a "taste" of Madrid and perhaps return there. (I certainly liked it.)

Thank you Sandancisco. Yes, originally had Sevilla as 4 nights and Barcelona as 5 nights & we had an extra 2 nights not allocated so added one each to those places with the view that they would be a base for day trips. We did think about an extra night in Granada, as one day will be dedicated to Alhambra, so I think we may be taking your advice and doing 3 nights there.

Thank you for your feedback Dick & for the suggestions of day trips...they look right up our alley! I am open to renting a car to get some experience off the beaten track, either for a day trip or an overnight. I'd be keen to consider some options only accessible by car from these bases if you think it would really elevate our special Spain trip.

My suggestions based on renting a car . . .

2N Cordoba from the airport. It's smaller, lower key than Sevilla, less stress while you get over jetlag and adjust to the time difference.
4N Sevilla. Rent a car and drive through the hill towns via Arcos to
2N Ronda. (take back the 2N you gave to Sevilla and Barcelona) Use the full day to see Ronda's sights and/or spend more time driving (very scenic) and seeing more hill towns. Leave early. Options on the way to Granada include visiting the prehistoric dolmens just outside Antequera, hiking in El Torcal. Drop the car in
2N Granada. Plan to get here fairly early in the day so you have time to see sunset from Mirador de San Nicolás. Be sure to reserve your Alhambra tickets before they sell out.
5N Barcelona

There is so much to see in Spain and you only plan to a fraction.

You are skipping the most awesome place in Spain, Toledo, the old capital prior to the 16th Century, when it was moved to Madrid. Also, Madrid deserves a day or two as well as a day trip to Segovia (another medieval city with a 1900 year old intact Roman Aqueduct).

Seville is wonderful, but you could cut a day or two there as well as a couple of day in Barcelona.

Hate to add more places to your list, but this blog by Cameron about Central Spain had me yearning to visit Toledo & Segovia. https://blog.ricksteves.com/cameron/2018/05/postcards-central-spain/

A few general observations:
[] It was good of you to time your itinerary by nights (which is precise), rather than by days. I would recommend this practice to everyone who posts an itinerary question.
[] For someone who expressed an interest in getting off "the beaten track,” you picked a set of destinations that are all solidly on it. Nothing really wrong with this; they’re all great destinations — just be aware that you probably aren’t going to be treading very far along un-beaten tracks.
[] Toledo, mentioned in a comment above, is a great place to see -- it's worth considering as a substitute for any of your original destinations that you might consider expendable. And I’ll agree that it would be a candidate for Spain’s “most awesome” place; but on whether it actually is, opinions differ. Spain is a great country, and tourists do come to have their various superlative preferences (mine, based on a 2009 visit, is Teruel), and a good use of this forum is to see what those preferences are. But in general, I would wait until, say, five or six more people designate a place as “most awesome” before altering a full itinerary to include it.
[] Itineraries tend to lean towards (1) seeing as much as possible, even if it means running around and just glimpsing some of it, or (2) relaxing travel with local “immersion” (as you put it well), even if it means seeing fewer places. As you seemed to hint that you lean towards the second option, you may find two nights in each of Cordoba and Granada to be a bit brief. This is probably all right, but if you are as seriously interested in local immersion as I am (and you may not be), you might stick to your four original destinations, but consider spending three nights in one of them, and four nights in each of the other three.
[] Finally, I would stick with the trains, as I presume you intended to. As for renting cars: one bad car collision, or even a big ugly scratch that appears on your car after it has spent hours in a cramped parking lot, and what should have been a relaxing trip suddenly ceases to be any such thing.