How quick could i get 15mgs of hydrocodone out of my system?

You can't: If you are using drugs not by prescription, and you know that you might be tested, that (to me at least) is pretty strong evidence of a drug problem. I would recommend being more concerned about your use of drugs than with being caught. Modern testing can detect adulteration of the sample or people taking in large amounts of liquids to "flush" it out or put the concentration of drug way down.