we know that
An exponential function is a function where the input, x, appears in the exponent.
the equation of an exponential function usually looks like:
[tex] y=ab^{x} [/tex]
where
a is a number called the initial value
b is a number called the growth factor
In this problem
we have
[tex] f(x) =\frac{1}{5}(15^{x}) [/tex]
where
[tex] \frac{1}{5} [/tex] -------> is the initial value
[tex] 15 [/tex] ------> is the growth factor
therefore
the answer is the option
[tex] D. 15 [/tex]
