The interest rates on these loans vary daily. Different lenders sell their loans to different investors at different rates.
So even on the same day, Wells Fargo might have a different 30 year fixed rate than Washington Mutual.
Another consideration is the fact that there is no universally accepted minimum interest rate. Rates can be “bought down” below the regular going rate that most people are getting.
So a I apologize, but this question will be answered with averages. From my education, the lowest period for mortgage rates was around May of 2004. In the 60’s and early 70’s rates were also quite low.
But in the spring and early summer of 2004, one could obtain a 30 year fixed for around 5%, sometimes 4.875%. If you bought the rate down it could have gone as low as 4.5% perhaps lower depending on the lender and how deep your pockets were.
In general, one can obtain a 15 year fixed for about .25-.375 less than a 30 year fixed all other things being equal.
Here’s a handy link: http://www.mortgage-x.com/trends.htm