Here is some impression over PT25 vs. PT15:
PT15 is known for its good detail, fast speed, clean and slight bright sound, but the PT25 is tuned quite differently. Instead, it is more toward a warmish sound that centered around a good mid range. Vocal is well textured and weighted, giving a more thicker sound when compared to the lighter PT15. Needless to say PT25 doesn't quite have the same quantity of air as PT15, but in exchange it has a sweeter and more intimated vocal. Lower end also improved, though I won't call it bass heavy in any way. Treble, as expected from the warmer sound, isn't quite detailed as PT15, but not lacking either. In sum, it is a switch from the (more or less) analytical sound of PT15 to a more classic warm+smooth sound signature. As far as overall SQ goes, I reckon it is a small upgrade but stays within the same general level. One area of improvement is ergonomics - as much as I don't like Apple's products in general, the earpod'ish design is indeed very comfortable.