Is mountain bike good for long distances? I am currently living in a plane area. I use an MTB (mountain bike). My work place is 10 to 15 km away from my home. Temperature is around 36 degree in celsius in my region.

Question : Is mountain bicycle good for this purpose?

Edit: See the image of mtb below. One more thing roads are straight but there are few up and downs in my ways.
10-15 km is not a particularly long distance. You can certainly ride and MTB on roads to commute to work. Obviously an MTB will not be as efficient to ride as a bike designed for road use (such as a flat-bar commuter, road oriented hybrid or drop bar road bike).

You can make your MTB more efficient by fitting narrower tires with a road tread (or no tread) and inflating them to the higher end of their pressure range.