USB-C to MagSafe 2 Adapter I have a 2015 MacBook Pro with a MagSafe 2 charging cable. My wife has a new MacBook Pro from 2016 with USB-C. I was wondering whether I could technically (in the matter of electronic feasability) use her charging cable on my MacBook and vice versa with some sort of adapter / dongle, and, if so, where I would get one?
You don't want to mix those two.

Why?

Because the USB-C port conforms to the USB 3.1 Power Delivery Specification whereas the Magsafe charger does not.  Part of that specification includes the negotiation of delivered power.  The Magsafe will not negotiate how much power is supplied.  What it's looking for is the presence of the 1 wire charging circuit before it begins charging.  

There may be adapters/converters on the market that will convert one interface to the other and vice versa, but (IMO) those cheap adapters are not worth the risk of sending the wrong voltage to your very expensive MacBook Pro.

Bottom line, use the genuine adapters built and designed for your MacBook Pro.