connection between sat radio and navigation???

SiriusXM radio has nothing to do with Navigation. If it expires ( as I let mine expire ), nothing will change other than listening to Sirius. Everything else will work.

 

That's Entune. I have a 2013 model 3 which probably isn't as advanced as yours.

 

The answer will depend on if your 2015 Four has a solar roof. If it does not (like mine), traffic comes from Entune via your cell phone. If it does, traffic comes from Sirius XM with a three year traffic data subscription.

 

I am no expert, but I believe traffic data is provided 2 ways; one through the Entune app by a company called INRIX and the other though HD data in the Top 100+ markets. The Entune app works when your cellphone is paired with the Prius via Bluetooth. The HD data comes through the HD radio. If Entune is not active, you lose traffic alerts when outside the HD coverage areas. If in the coverage area, there is supposed to be an HD icon in the upper left of the display. As lumpy said, I believe all you lose is SiriusXM radio service if you don't renew your subscription after the 90 days.

FWIW, we take several cross-country trips each year and enjoy SiriusXM service, especially Phlash Phelps and his "60's On 6" morning program, so the subscription is worth it for us. Before your 90 days is up, you should get a renewal notice with discounted rates vs the standard rates on their website.

Traffic

Edit: I don't have the Premium nav, so I don't know about the XM-based service. I could be wrong, but I think the ones I mentioned will still apply if you elect not to continue the XM traffic subscription after it's 3 year free run.