The average interest rate on a 30-year fixed mortgage increased to 6.72% from 6.6% last week.The average rate on a 15-year fixed mortgage remained steady at 5.73%.Borrowers should compare their existing mortgage rate with current market rates before refinancing.The APR on a 30-year fixed-rate mortgage is 6.75% and for a 15-year fixed-rate mortgage is 5.78%.