Is it possible to have more fireflies at the same time I use more samples? I am referring to the white dots that appear in glossy objects. 

I moved a little the metal carpentry for the second image, and I got less noise in the horizontal ones which are on the top, but for some reason, dots appear in the vertical one, and also in the one that is from the terrace, which is outside, and I didn´t change anything to it. 
The first image has 1200 samples and the second one 1800.
First I would recommend checking to see if you are using any small light sources. A sun should be fine but small spotlights and things of that nature can cause fireflies.
Blender Guru has a solution to fireflies. As to why the amount of samples cause more fireflies is strange,  but you are working with a complicated scene.
Blender Guru Fireflies