Average 15-Year Mortgage Rates. Here are the current average 15- year mortgage rates in each state. Average 15-year fixed mortgage rates tend to be lower than rates for 30-year home loans. While this does mean less money spent on interest, the monthly payments on a 15-year loan are consistently higher in all states. Historical Mortgage Rates. National Average Contract Mortgage Rate: Index History. National Average Contract Mortgage Rate For the Purchase of Previously Occupied Homes By Combined Lenders. The National Average Contract Mortgage Rate is derived from the Federal Housing Finance Board's Monthly Interest Rate Survey (MIRS). National monthly average rates are derived from HSH's database of 2,000 to 3,000 lenders. (3) Federal Housing Finance Board's Monthly Interest Rate Survey, National Average Contract MortgageRate (the Contract Rate on the composite of all mortgage loans, fixed- and adjustable-rate, derived from the Federal Housing Finance Board's (FHFB) Monthly