How can I sue someone that owes me $15,000 and I have notarized loan contracts

You would draft a complaint setting foth the basis for the court's jurisdiciton and your claim, you would draft a summons (forms can be found on the court's website), you would buy an index number online and efile the summons and complaint.  Then you would cause the defendant to be served with the summons and complaint.  For more details, you should contact the clerk of the court.