Welcome to a world of elegance, Balmain Watches, from the stable of the world’s largest watch-making conglomerate, the Swatch Group. Extreme elegance and irreproachable quality: the world of Balmain is unique.
This is clearly advertising copy - there's nothing really wrong with the grammar, but the punctuation and choice of words could perhaps be improved. This depends on how the message is displayed and the context.
Irreproachable is not a a well-used word so doesn't immediately communicate the meaning. I'm not sure what is meant by The world of Balmain is unique. Everything is unique, so why not come up with some other aspirational statement such as The world of Balmain is your world.
I would do something like this:
Welcome to a world of elegance
From the stable of the world’s largest watch-making conglomerate, the Swatch Group, Balmain Watches represent extreme elegance and ultimate quality.
The world of Balmain is your world
Note that I've omitted as much punctuation as possible - each style change gives the emphasis and pauses you need.
Hope this helps.