By the Rational Zero Theorem, if p/q is a rational zero of the given polynomial, then p is a divisor of the constant term, -15, and q is a divisor of the leading coefficient, 5.
So, the possible values of p are: ±(1, 3, 5, 15) and the possible values of q are: ±(1, 5). Therefore the possible rational zeroes are:
±(1, 1/5, 3, 3/5, 5, 15).