Rates on 15-year fixed mortgages have dropped for a third consecutive week, according to Freddie Mac. The rate averaged 4.47 percent, the lowest seen since Freddie Mac first began reporting mortgage figures in 1991. Meanwhile, 30-year fixed mortgage rates, which averaged 5.04 percent, also dropped this week from 5.07 percent. These figures could put 2009 on track to have the lowest mortgage rates in several decades, according to Frank Nothaft, chief economist with Freddie Mac. “Interest rates for 30-year fixed-rate mortgages have averaged just above 5 percent through mid-September, which is roughly a percentage point below last year’s average and suggests that 2009 may reach a record annual low since the survey began in 1971,” Nothaft said.