Reloading fixed the problem.
Old deprecated server behaviour was already there when I reloaded DW cc2015, I removed Webassist Mysqli server behaviour and then reloaded the app It worked!. Somehow Webassist installer didn't kick in previously. I am using php7 server on this computer in order to rewrite php code in php7 I hope everything will work ok with php7 server. Thank you anyway for help.