If the fluid level is checked it's a good idea to measure what comes out and goes in so you know if there was an issue there.
Doing the check yourself is maybe a bit harder than I said. You need to be able to safely support the car at the right level with a wheel off. I park the car on a known level surface and put a circular bubble level somewhere on the car, then jack to keep the bubble level.
Doing it with one jack is potentially dangerous, one mistake with the footbrake and you're lurching forward.
It's easy for me because I use two trolley jacks up front and lift the rear as well. And I've plenty of time to muck around.
It does sound like a new
TCM if you are getting P0715. That's the Ford manual injunction anyway. I suggested checking fluid level as a first step in general with gbox issues, but seems to me less likely to be connected with the P0715.
That's my googling and guessing anyway.