Thirty-year fixed-rate mortgages averaged 7.54% this week, up from 7.46% last week, according to a national survey released by the Federal Home Loan Mortgage Corp. It is the highest since July 3, when rates averaged 7.62%. They dipped to 7.36% on July 31, but have risen during the last two weeks. On one-year adjustable-rate mortgages, lenders were asking an average initial rate of 5.56%, up from 5.53% last week. Fifteen-year mortgages, a popular option for those refinancing mortgages, averaged 7.07% this week, up from 7% a week earlier. The rates do not include add-on fees known as points.