That is not true. The Lenin-Liebknecht-Luxemburg Demonstration has been a thing since 1919 to honor the deaths of these revolutionaries and has been a big state event during the existence of the DDR. It's independently organized by revolutionary organizations from all across Germany. The Junge Welt and the Rosa Luxemburg Konferenz has only been a thing since 1996 and is something completely different that happens on the same weekend. Both the RLK and Die Linke (left non-revolutionary socdem party) are somehow trying to claim this event.