Answer
$7.5*10^{-4} \ \text{bar*s}^{-1}$
Work Step by Step
For a reaction $aA(g) \to bB(g)$, the change in pressure will scale by moles according to Dalton's law
$\frac{\Delta P_B}{\Delta t} = \frac{b}{a}*\left(-\frac{\Delta P_A}{\Delta t}\right)$
In the case of this reaction:
$\frac{\Delta P_{O_2}}{\Delta t} = \frac{3}{2}*\left(-\frac{\Delta P_{O_3}}{\Delta t}\right) = 1.5*5*10^-4 = 7.5*10^{-4} \ \text{bar*s}^{-1}$
