RE: 2315 or somthing else
2315 pretty much fills a void that no other aluminum arrow size can fill. Good blend of accuracy, trajectory and durability. The larger diameter, thinner walled and lighter arrows might flatten your trajectory a tiny bit, but they don't have anywhere near the durability the 2315 gives. It's one of my favorite arrow sizes.
To get a light enough arrow to noticeably flatten your trajectory, you'll have to go carbon.