Right wireless tech for 1.5Km with LOS but small-power availability at remote end?
Also consider LoRa sub-G RF modules: long-range, battery powered (ULP), ISM band, affordable price. Many modules are available (though chipset mostly by Semtech, seems also Microchip is offering recently). Quick search returns:

https://www.cooking-hacks.com/documentation/tutorials/extreme-range-lora-sx1272-module-shield-arduino-raspberry-pi-intel-galileo/

http://modtronix.com/inair9.html

http://www.seeedstudio.com/s/LoRa.html

https://www.loriot.io/modems.html