I suppose it would depend on riding conditions. In the snow or mud you would want wider tires. Thin tyres are suppose to offer less rolling resistance, just ask the endurance cyclist. For ebikers, i doubt we are on these things long enough to appreciate any major difference.
Another point, i recently discovered the sizes you mention, refer the the width of the wheel rim where the bead sits. Assuming you intend to use the same wheels, you might find the 1.5 tyre a loose fit in the rim of a 1.95 wheel.
I wait to be corrected.