It really depends on what your priorities are. Do you want a machine that will be supported for a longer period of time? Or do you want the big savings now? The 2015 13" MacBook Pro with 8GB of RAM and 256GB of storage is currently $1,399 (from what I can see in the refurbished section based on savings of 15% for a final price of $1,189), while the new MacBook Pro with 8GB RAM and 256GB storage is $1,799. That's a $400 increase, and what does it get you? You get a thinner and lighter machine, a newer CPU, faster RAM, updated Intel graphics, a larger trackpad, brighter display, TouchID, OLED Touch Bar, and new USB-C ports.
I think the value proposition of the new MacBook Pro is pretty good, and about equal to that of the previous generation, given that they did not announce a price drop for the outgoing models.