I'm looking for a formula that will calculate the following information:

If 15% of the sum of a range of cells is less than $40.00 then the fee is
$40.00.
If 15% of the sum of a range of cells is $40.00 or higher, then the fee is
15%.

I hope that made sense.

In other words, the fee is 15% or $40, whichever is higher.