Depending where you are on the planet, the poles it's 6,357 km to the center of the earth and the equatorial maximum of about 6,378km
So we have a point where to pivot the arc.
Earth circumference is 40,075 km
So we are positioning the second tower 10 meters away from the first one. This works out to be 0.00024% of the earth diameter away, which is 0.0898315degrees
The tower is 1500feet which is 457.2meters
So the top of the tower would be measured as a circumference of 40532km. Multiply the the degrees difference which is 0.0898315 then divide by 360.
We get 10.11 meters. So the difference between the bottom of the two towers and the top is 11cm
There is a slightly more accurate way of doing it, using arcs, as I was taking a straight line measurement between the two towers not an arc, which would give a slightly more accurate number.