The average interest rate on 30-year, fixed-rate mortgages slipped to 8.22% this week, down from 8.32% the week before, Freddie Mac said. Fifteen-year mortgages dipped to 7.91%, down from 8.04% last week. On one-year, adjustable-rate mortgages, lenders were asking an average initial rate of 7.21% this week, down from last week's 7.24%. The rates do not include add-on fees known as points. Meantime, the Mortgage Bankers Assn. of America said mortgage loan applications last week fell 6% from the previous week and were down 17% from the same period a year ago.