Answer
$\approx 1.953445$
Work Step by Step
RECALL:
The change-of-base formula for logarithms:
$\log_b{x} = \dfrac{\log_a{x}}{\log_a{b}}$
Use the formula above and use base 10 to obtain:
$\log_4{15} = \dfrac{\log{15}}{\log{4}}$
Use a scientific calculator and round-off the answer to six decimal places to obtain:
$\approx 1.953445$