GUSTO took over the former channel position belonging to MuchMoreMusic (last known as M3) across major cable providers on September 1. Bell Media shut down M3 in favor of GUSTO.
I can't confirm exactly why WNED (PBS) is now airing on both channels. My guess is, if you're in southern Ontario, channel 15 in previous years belonged to the now-defunct CityNews Channel which ended in 2013. Afterwards, it became a Free Preview channel and it looks like that has changed over to WNED (PBS). Probably not all Rogers Cable subscribers have access to positions higher in the dial, so they are also carrying it on channel 15 as analog TV lineups continue to be gradually phased out across different areas.