Which stereo in which Forester? There were three or four different ones available for the 2015, ranging from the old-school Clarion in the base unit to a touch-screen Harmon-Kardon with navigation available in the Touring and Limited.
I think most people would suggest that if you're replacing the head unit anyway, choosing something that would be an upgrade over the famously substandard Subaru units would be the way to go.
I recently replaced the Clarion in my '15 Premium 2.5i with a Sony XAV-AX5000, and could hardly be happier. (I'm not alone in doing this sort of thing which is why so many used Subaru head units are available on ebay.) A new unit will have Carplay/Android Auto, better electronics for better sound, better Bluetooth performance, a nicer screen, and other worthwhile improvements.
The details of course depend on which Subaru head unit you're replacing.
I think most people would suggest that if you're replacing the head unit anyway, choosing something that would be an upgrade over the famously substandard Subaru units would be the way to go.
I recently replaced the Clarion in my '15 Premium 2.5i with a Sony XAV-AX5000, and could hardly be happier. (I'm not alone in doing this sort of thing which is why so many used Subaru head units are available on ebay.) A new unit will have Carplay/Android Auto, better electronics for better sound, better Bluetooth performance, a nicer screen, and other worthwhile improvements.
The details of course depend on which Subaru head unit you're replacing.