The Place Catalogne is actually in the 14th, though not far from the 15th. On one side of it is Montparnasse and all its train tracks, and the other side is pretty much an ordinary Parisian middle-class neighborhood as far as I can tell, though I've always been there during the day and early evening hours so can't say what it's like later at night.

Would you mind sharing why it should be avoided, according to what you've heard? I admit that surprises me, so I'm curious to know the reason behind it.