@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:
Open Xcode and type something, it works :)
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.