How low can we go? When it comes to mortgage rates, the floor keeps dropping. Industry reports released Thursday show that interest rates for home loans - already at their lowest marks in more than a half-century - dropped again this week. Market analysis conducted by Freddie Mac puts the 30-year fixed rate at 4.32 percent and the 15-year rate at 3.75 percent. Bankrate says rates for the larger jumbo 30-year fixed mortgage also inched lower to 5.16 percent.