The sum of the following series 

$1+6+\frac{9\left(1^2+2^2+3^2\right)}{2}+\frac{12\left(1^2+2^2+3^2+4^2\right)}{9}+\frac{15\left(1^2+2^2+.....+5^2\right)}{11}+....$up to 15 terms, is