Answer
The answer is $3a-5$.
Work Step by Step
$(-16a-15+15a^2) \div (3+5a)$
$=(15a^2-16a-15) \div (5a+3)$
$3a-5$
_________________________
$5a+3)15a^2-16a-15$
$15a^2+9a$
_________________________
$-25a-15 $
$-25a-15 $
_________________________
$0$
The answer is $3a-5$.