Macbook Pro Differences (2015 vs 2016)
The 2016 model's probably going to have Thunderbolt 3 which is usb-C compatible. It's quite possible that it's going to have a complete redesign and some of the ports like HDMI and SD-card slot might have to go. With Skylake there's going to be new Iros Pro integrated graphics which compete with current dGPU's of suitable thermal envelope for the MBP. As there's nothing significantly better available I think they are going to ditch the dGPU option for good and make the chassis smaller and lighter.

AMD's Polaris and Nvidia's Pascal are coming in the second half of this year and they are going to outperform Iris Pro but I doubt Apple is going to wait for them as they are not so keen on ultimate graphics performance.

The next Apple event is going to be March 21 and there has been no solid rumors of anything that's going to be announced there. I believe we might see the new MBP there because there's really no reason for Apple to keep waiting when competitors are adopting the new high-end Skylake processors. A lot of retailers have the 2015 model on discount right now and their stock is running low. 

If you dont't think you need a slight improvement in performance, the possible redesign and Thunderbolt 3, now is the time to jump on those discounts. The 2015 is by no means a bad laptop.