Easy product :)

Algebra Level 2

$x = (1-\frac { 1 }{ 2^{ 2 } } )(1-\frac { 1 }{ { 3 }^{ 2 } } )\quad ...\quad (1-\frac { 1 }{ { 15 }^{ 2 } } )$

If $x$ can be written as $\frac{ a}{b}$ where $a$ and $b$ are positive coprime integers, what is the value of $a+b$ ?