depends on the cymbals.  if everything else is the same, yes, there will be a difference.  ive found that 15's have a less pronounced "chick".  they also tend to have a louder, deeper sounding "slosh" when half open.  for straight ahead rock the 15's will give you a heavier meatier sound.  they may lack definition for more intricate stuff.  

i primarily use a 15 top with a 14 bottom.  nice dark, warm "slosh" due to the 15, but because of the smaller bottom they have a more pronounced "chick" than a 15 pair would have.  ive tried a thin 16 on top of a 15 and if i was playing heavy rock i mightve stuck with it.  great fat wet sound, but very little "chick" to speak of.  also a normal 14 pair with a great "chick" and relatively clean "slosh".



i have two wuhans, a 12 and a 20.  and im working on making another, less trashy, more gongy one out of an old 18 crash.  

i dont use them with my pop band because im going for a more open, quiet, etherial sound with them.  and the chinas are a bit brash and fast for that (though the new one im working on might fit).  but with my improv stuff i use 'em often.  the wuhans are too much for any type of riding but for accents they are great.   and that 20 just roars like an angry beast when you bow it

all in all china's are a great color option.  and options are good

14's are FAR more common than 15's, even in heavy music. And they take up less room, which can be a factor in large complicated drumsets.

Most people mount Chinas upside down if they primarily plan to crash the cymbals, whereas a lot of jazz drummers mount them right-side-up, and play ride patterns on them.

Most Chinas have upturned edges, which chews up the sticks more if you play them right-side-up, and could make the cymbal more susceptible to cracking, since it would be getting hit on its edge all the time.  

Also, the sound is a little more controlled when you mount them upside down, as the way they balance on the stand tends to restrict their movement a bit.

Aside from my 15" New Beats, I haven't seen 15" hats around here at all, and I love it that way.