Electronic – Wireless Module with over 1.5Km range

You ask about the Xbee-Pro 900.

As the name suggests this works in the 900 MHz. The datasheet mentions a LoS range of 3 km, but since you don't have LoS that may be considerably less. The module has an RF connector, though, so you can connect an external high-gain antenna, which, again according to the datasheet, would increase the range to 10 km LoS. Should be enough for your application.

Your link is to an eBay reference. I wouldn't buy from sources like that. For Sri Lanka Digi has a distributor in India, which will probably give you better support. (Many product you buy on eBay you can't get any support for at all.)

Further reading
Xbee-Pro 900 Manual

I'm designing a wireless device now and have looked through different options. Now i'm deciding what to use between two choices:

• Sub 1GHz radio chips or modules such as RFM12B or Silabs Si4455. They are very cheap and can give a good range of about kilometer. But if your base station is, say, 2km away from one of wireless devices — it will be no link because this modules don't give you a mesh. You have to code it by yourself.
• ZigBee modules or SoC like Atmega128RFA1 can have a higher price but give you ready to use MAC addressing and Mesh network. Mesh netwok allows you to connect two devices, which have no direct link, via third device in between of them. This allows you to build large-area wireless netwoks. Also ZigBee is known for very small power consumption.