@hamzasood (Thanks!) mentioned about hidden feature in Xcode7 - Fuzzy Autocompletion.

Finally Apple added it to the Xcode. I think they will release it as new feature in Xcode 8. You can turn it on manually if you want. Just quit Xcode first, open terminal and paste:

defaults write com.apple.dt.Xcode IDECodeCompletionFuzzyMode 3

Open Xcode and type something, it works :)

image-1

UPDATE:

Setting this key does not work in Xcode 7 beta 4.

To make it work in the newest Xcode you have to set IDEWorkaroundForRadar6288283 key instead of IDECodeCompletionFuzzyMode.

defaults write com.apple.dt.Xcode IDEWorkaroundForRadar6288283 3