Convert 1815ft to meters (only because I only know the gravitational constant as -9.8m/s^2

1815 feet = 1815 feet * 0.3048 meter / 1 feet = 553.2120 meters

So, initial velocity we'll assume to be 0m/s position is 553.212 meters and gravity is -9.8m/s^2

p = p0 + v0 t + a t^2

0 = 553.212 m + 0 t - 9.8m/s^2 * (t^2)/2 solve for t

4.9 * (t^2) = 553.212

4.9 * t^2 = 553.212

t^2 = 554.212/4.9 = 112.9

t = 10.6255 seconds. (Actually, +/- 10.6255 seconds, but that would say that you _launched_ the object straight up from the ground at t0-10.6255 seconds, it reached it's (apogee?) at 1815 feet at t0, and then came back down at t0+10.6255 seconds.)