Big Drain-to-Source voltage in MOSFET
Look at this in the data sheet (I've drawn a red line on at 1.5 amps): -



These are typical values and what they tell me is that if your Vgs voltage is more like 4.5 volts then you'll never drive the motor properly. At 5 volts it should be OK but probably at somewhere between 4.5 volts and 5 volts you might see 3 volts dropped from drain to source.

Remember these are typical numbers and for the particular device you may have you might need a little bit more than 5 volts to achieve what you want. You should also remember that this device isn't a low on-resistance type - even at 5 volts and 1.5 amps drain current, the volt drop from drain to source is a fraction over 1 volt and you will be dissipating over 1.5 watts of power.