Also, gravity has minimal effect, so the laser will always travel in a single dimension (straight). Horizon would prevent it from going much more than 15 miles directly across the land (which will not be an issue as it's pointed UP). If fired in a vacuum (like space) the range would be significantly increased.
and here you are wrong, photons are subject to gravitational pull... you know black holes suck in light? well it will bend here on earth too if the distance is great enough, if you shoot a laser past the moon then it will bend in behind the moon as well.