What are you trading? The RD's or the Kickers?
All things being equal, the 15" sub is generally louder than a 10" sub (stupid laws of physics!)
Not going to argue with Mr. Anywaypasible, but I disagree with quite a bit of what he is saying. At least in the context he is putting it.
Subwoofers performance is entirely dependent on the enclosure they are mounted in. A bad enclosure design can make a 1000 dollar sub sound worse than a good design and a 20 dollar walmart sub that you bought third hand at a flea market.
As for amplifiers, today even off brands can be decent as long as you are running them within their true power capabilities and you feed them enough power from your electrical system. The planet audio amp should do fine. As we don't know the model number to determine what the amp can actually do or if it is stable to drive your subs, as long as you keep it within its capabilities it should survive and give you plenty of good bass.
If you are trading to get the 15's, remember that they are going to require a bigger enclosure than 10" subs.