Dual rates (d/r) are usually referred to as high rate and low rate, or just "High" and "Low".

Plus/minus 1.5" on low rate elevator would mean that with the d/r switch down, full throw on the elevator would be 1.5" up and 1.5" down. Sometimes there will be an aileron recommendation for more throw up than down. With the d/r switch flipped up (on high rate), the elevator travel might be 2" up and 2" down (plus/minus 2" ).

Good luck,
Dave Olson