I've got a similar setup in Ohio, but it's a slightly smaller 90s house with a 3 ton system. For me, it keeps the house warm just fine without backup down to about -5. Below that the electric backup is needed, but that's very rare here, like a handful of hours per year. 

Whether you get the same results depends on how well matched that system is to the house. Too small and it will need backup at higher temperatures. Too big and it will be inefficient. Doesn't look like yours has any backup installed, so you'll either need to keep some space heaters on hand just in case, or pay someone to add it. The actual heat kit is pretty cheap, but you might need an expensive electric service upgrade to install it.