Why do your solar panels produce only 5mA? Mine from cheap solar garden lights produce 40mA.
Each of your solar panels appear to produce 2V then why did you connect them in series to produce 15V at hardly any current? In parallel they will produce 2V at 45mA or more.
A 1.5V AA battery can supply hundreds of times more current than your solar panels.
Use a much larger solar panel but you want more current, not more voltage than the motor needs.
One or a few paralleled solar panels like you show can charge a little AA Ni-MH rechargeable cell all day in the sun that can power the 1.5V motor.