Seeing how OP said that the anticipated ownership is 105K miles over 15 years that’s pretty darn close to a negligible difference. Now, add in at least one brake job (likely two) for the non-hybrid. And if they are elderly and likely bringing it to the Lexus dealer for that brake job, now you are looking at an additional $800 minimum in additional maintenance for the non-hybrid. Hybrids are also stupid easy on their 12V batteries because they are only used to throw one relay on the traction battery. Our 2010 Ford Fusion hybrid is on its factory battery at 190K. It has been testing as “bad” for about 8 years, but it still turns the car on.
If they live in a warm environment, a hybrid will also be much more comfortable if they do any amount of sitting and idling in the car. Hybrids will shut off their engine and idle with the air conditioning going for roughly 10-25 minutes before having to kick their engine back on. Traditional cars will idle the motor the entire time.
As for low-mileage drivers preferring non-but did, I’d say it depends. My mom was a 2-4K mile per year driver towards the end and she loved her hybrid. As her mobility issues ramped up, she was able to get food with my father or the grand kids at a drive-through and then sit with the engine off while they ate. She was also able to drive to local parks with the grandkids and while the kids were playing, she was able to sit in the car with air conditioning; zero gas burned.
When dealing with retirees, you can’t simply break things down to “ X will be $500 cheaper overall over 15 years”. Think of the creature comforts and whatnot. OP, have them drive both cars and take cost out of it. See which one they like more.