To factor $ 6x^{3}+9x^{2}+10x+15 $ we can use factoring by grouping:
Group $ \color{blue}{ 6x^{3} }$ with $ \color{blue}{ 9x^{2} }$ and $ \color{red}{ 10x }$ with $ \color{red}{ 15 }$ then factor each group.
$$ \begin{aligned} 6x^{3}+9x^{2}+10x+15 = ( \color{blue}{ 6x^{3}+9x^{2} } ) + ( \color{red}{ 10x+15 }) &= \\ &= \color{blue}{ 3x^{2}( 2x+3 )} + \color{red}{ 5( 2x+3 ) } = \\ &= (3x^{2}+5)(2x+3) \end{aligned} $$