Is there a real significant difference when it comes to a 16lb ball vs. 15lb ball?  Does one pound really matter?  I know that you're supposed to throw the heaviest weight possible that you can carry.  Please give me your opinions.  

There really is not much difference in hit at all.

I can give you 2 examples, one being good to drop in weight, the other being bad.

example #1
My dad, older guy, he has lost the revs he had gotten on 16lbs and his speed was down to nearly 13ph. I bought him a 15lb ball and at first he hated it (I think he took it as a blow to his manhood). I made him start using it more and he loves it. On average his speed is up to about 14.5mph and his rev rate is definately up. He gets great carry out of it, and still gets the strong hit.

example #2 ME
I throw 16lb equipment about 20-21mph. I tried 15lbs once and I threw it nearlly 25mph. I have a great rev rate on both 15 and 16lbs, but my speed usually counters that. So, unless I am on drier conditions 15lbs is a definate no no.

I can echo what Excalibur said about ball speed. Since I am not a little guy and can create ball speed without much effort, 15s are a no no for most conditions. What I have found is that if I use 16's most of the time, when the drier conditions show up the lighter weight does not hurt my timing. When trying to use exclusively 15's my timing suffered. I actually leave more 7 pins with 15's than with 16's and probably more solid 10's with 16's but weak 10's with 15's. If the lighter weights fit your timing then go with the lighter. If not, well go with what works. I still in my arsenal have 16's, one of my favorite balls is actually a 15-4, and then I have some 15's. Normally the drier the lighter, but one of my best drier lane balls is a 16. Depends on lane surface and what is providing the best reaction and carry. Hey that is the bottom line. What is carrying best. I also use either a 5 step or 4 step delivery and if too deep a 3. Again, depends on what is working or the lane equipment allows (ball return). Do what works for you. I have friends that use 14's and they work fine on house conditions most of the time.