Xcode 7 performance issues
Since you are developing - fire up Instruments and use it to profile Xcode. 

You'll need to determine if storage/io is the cause of the slowdown or if it's CPU or if it's network.

From there, you can ask a follow on question once you have some data on the problem. My guess is Xcode could be downloading the new documentation - check for intalld/active network downloads. Or it could be symbolicating crash logs from all connected devices, or downloading symbol tables from connected devices, or running a sandbox, or ...

Basically, since Xcode is so large a tool, it's hard to know what subsystem you are even using without some data.

FWIW - here's a properly behaving, no simulator running, a dozen other apps running, Xcode done installing documentation Xcode using a hundred meg of RAM while open.



The Mac in question is up 3 days and has has a lot of mongodb and VirtualBox linux VM running which make the kernel larger than it would be at boot, but even that isn't causing any sort of memory pressure.