my point about the CAE
's is that they will get too big to be in just a 15 gallon tank. They can reach 10 inches. Here are some quick stats on this. This site is pretty reliable for information, even if their prices are WAY too high.
And for the rosy barbs, they are some of the largest of the barbs, reaching about 6 inches. They also like being in groups 3 so they'll be either too big to go with the rest of your fish, or you can just squeeze three in your 15 gallon, but I think you'll have a problem with aggression once they get older.
Now, cherry barbs would work (good suggestion Fishlover14). They only reach 2 inches and even though they need to be in a small group, they'd do well in your 15 gallon. Of course, they might be nippers, but I don't know about that.