Use this formula for your problem:
FV=P{[1 + R]^N - 1/ R}=FV OF $1 PER PERIOD. Where R=Interest rate per period, N=number of periods, P=periodic payment, FV=Future value.
FV=300{[ 1 + 0.06/12]^15 - 1 / 0.06/12}
FV=300{[1.005]^15 - 1 / 0.005}
FV=300 x 15.53655
FV=$4,660.96
