I highly doubt that they were "completely overexposed" if you rated the film at EI 25 and metered off a grey card. Barring mechanical problems, they are probably overdeveloped. Look at your shadows to determine if the exposure was good or bad. Look at your development if the shadows are OK but the highlights are super thick. If you have trouble reading the neg by looking at it, take it to a pro lab and ask them to read it with a densitometer, and then come back here and post the readings from various parts of the negs. If your developer was D-76 or ID-11 1:1, then you developed about 150% of what would be approximately normal at 20C. Your specific water could also boost the activity of the developer somewhat vs. Ilford's testing, as could a thermometer that reads too low. You also may have agitated significantly more than your friends did with theirs. In short, it may be that you overexposed and overdeveloped an already-contrasty film shot in contrasty light, and on top of that, there are numerous other variables that could have contributed. This probably helped your negs in the flat indoor light, but not outside.
In my testing, medium format Pan F has to be rated at EI 16-20 in order to be able to place a tone on Zone I and get something there. It is an extremely contrasty film and does not hold shadow detail well unless you have experimented a bit with how to do it. Same applies to the highlights, so when you give it extra exposure, they tend to block up without some experimentation to find a decent development time.
I would try again at 25, but this time maybe try 8-10 minutes instead of 15, assuming D-76 or ID-11 1:1 at 20C.
Not that it will be applicable to you, but my normal developing time using HC-110 dil. B with the film (rated at EI 16 in one of my tested cameras and EI 20 in another camera) is 6:00 at 24C.