k²,
I know you didn't ask me, but whatever, I didn't think you would mind.
I always heard that you should never change the ATF in Fords, but I don't know why.
I had a MOPAR once that would not move in any gear but reverse. Had the shop change the ATF and filter and it ran fine until I got a new car. (Company car, I always do most of my own work on mine)
Seems to me 15 years is too long to go without changing it though.
I would smell the fluid on the dipstick. If it smells burnt at all, I would change the fluid and the filter.
BTW, what made you ask?
I am one that doesn't like to screw with things unless they are broken, but I also believe in routine maintenance.
I kind of walk a fine line since I have so many cars on the road.
Have fun,
Phil