I'm posting this because no one seems to discover this problem in iOS9, but it is critical.
The problem is simple, every time you call
sprite.runAction(SKAction.playSoundFileNamed("sound.wav", waitForCompletion: false))
a little bit of memory leaks.
It might not be such a big issue at first, but it will eventually slow down your games since the memory will NEVER be recycled.
Reproducing this bug is easy, just call this method in scene's update function, and you can watch it eating up all your memory.
The solution is simple too, replace the code with the new SKAudioNode for iOS9 and up, and you are good to go.
I Think this is one thing everyone should try first to repair one's game for iOS9.