WASHINGTON, Jan 15 (Reuters) - The U.S. Treasury Department on Friday began distributing $15 billion in new payroll assistance to airlines approved by Congress under similar conditions to an earlier round of aid. Delta Air Lines said it expects to receive $2.9 billion, with $830 million in the form of an unsecured loan. The airline said it received the first installment of $1.4 billion on Friday. Southwest Airlines said it expected to receive $1.73 billion in total and received $863.7 million on Friday. Major airlines must also issue warrants to the government as part of the assistance. Congress approved a separate $25 billion in payroll assistance in March. (Reporting by David Shepardson Editing by Chris Reese)