MOSFET controlled DC motor too slow
You need to use a MOSFET with a logic level gate. The MOSFET you are using is only slightly 'on' with 5V on the gate. It's not guaranteed to conduct more than 0.25mA at 5V Vgs. 

Get one that has a guaranteed Rds(on) at 4.5V gate-to-source voltage. For a motor with a run current of 150mA, maybe a few amperes at start-up, so &lt; 100m\$\Omega\$ should be okay. 

For example, a NDP6020P which is guaranteed to have less than 80m\$\Omega\$ with 4.5V drive even when very hot (125°C) and is more likely to be ~40m\$\Omega\$ at room temperature. 



Alternately you could re-design your circuit to provide a -5V gate drive wrt ground (-10V relative to the source) but even so that (high voltage) MOSFET you have isn't all that suitable with an Rds(on) that is about 10x higher. What it's good for is high voltage (-200V rating).