The term "Compound interest" on a mortgage loan confused me - I had never heard of that. Normally compound interest applies to interest earned (APY - Annual Percentage Yield) on a savings account.
I did a google search and came up with this very good explanation comparing a simple interest mortgage loan vs. a traditional mortgage loan. It is at www.mtgprofessor.com/A%20-%20Amortization/how_does_simple_interest_work.htm .
Looks like I have always had simple interest mortgage loans. I always made my payments early and when I came into extra money paid down the outstanding principal whenever possible so I have saved a lot on interest. With a simple interest loan if you make your payment on the due date or later over the life of the loan you will end up paying a lot more. If you can afford a higher payment, a 15 or 20 yr loan is much cheaper than a 30 yr loan.
The percentage rate, say 5%, is not 5% of the total loan, it is an "Annual Percentage Rate" of 5%. Look at your mortgage loan document. It should show the APR and the % in the blocks near the top of the form.
People that can't pay at least 20% down also get stuck paying Private Mortgage Insurance (PMI) for the first several years until the loan is paid down to about 80% of the original amount if it is a commercial loan. If I remember correctly, if you have a FHA loan you have to pay the PMI for the full term of the loan.