Is it possible to install Xcode 7 in 10.9 OS X?
If you really wish to remain on Mavericks and not upgrade to El Capitan I would suggest installing it on an external drive or partitioning your main drive just for a test. Make a new 60 gb partition(just in case you actually like El Capitan) and if you are not satisfied with its productivity, trash it. I guess you could use it just as a "developer" OS and switch to it only when you'll be using it but that in my opinion would be inconvenient. I am using El Capitan on 2008 MacBook Pro the OS itself runs perfectly. The startup is a bit slow compared to most newer computers and the CPU isn't the best(2x2.4Ghz) but it works fine for such an old machine.