That will depend a great deal on which 15 cent stamp it is. There have been stamps issued for many decades with that value. Consult a catalog and identify the specific stamp. It will also help you find the value.
8 cents.
The cost for postage in 2005 was 37 cents.
44 cents __ Depends on where the stamp is from. The price will be whatever the current postal rate is. It's not old or rare to be worth more than face value.
15 cents.
15 cents.
44 cents in 2012
20 cents.
The C stamp came out in 1981. It has a face value of 20 cents.
The first US stamps came in 2 denominations -- 5 cents and 10 cents.
They are probably worth 9 cents.
four cents
four cents