For me money is the issue and also, I do not have anything Type-C So, 2016 is out of the picture.
For me, it will be 2015 with slashed prices
About the display size. I am using 2011 17 inch MBP and it's slowing down. It has 1920x1200 resolution same as my monitor. So, even 13-inch MBP will be good for me and it has much higher resolution. If I want I can buy a separate 4K monitor,
With 2015 MBP 15-inch starting model, I believe we have 8GB option. So if the difference is not that significant between 13-inch and 15-inch, I will go for 13-inch.