First, according to different dictionnaries I checked in, sitting room, living room, and front room are all synonyms of lounge. However, it seems that lounge room is not recognize as a term to describe a room in a private house. It would be the expression you use in a restaurant or a public place.

A "lounge" was the anteroom to a public restroom, usually containing a chaise longue. This is just personal experience of U.S. Southern usage. Sitting room = British English and still used today. Lounge = not a living room. It's what might also be called a TV room. Lounge room sounds like an institution.

The younger you are, the more likely you are to call it the living room, as two thirds of millennials do. But the older you are, the more likely you are to call it the sitting room. Those who are middle-aged (35-54 years) are most likely to call it the lounge.