Thanks IIIaass for your reply. Here is my answers, and I put the links blow in case you would like to have a look.
2014 is 90 dollars more
Apple do not tell anything directly about discrete graphics, but they say that 2015 has:
Graphics
- Intel Iris Graphics 6100
- Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 3840 by 2160 pixels on up to two external displays, both at millions of colors.
2014 has:
Intel Iris Graphics without
Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 2560x1600 pixels on up to two external displays, both at millions of colors
I think that 2015 has discrete graphics and 2014 does not.
What applications can get benefit of discrete graphics???
they are both 8GB but 2015 is 8GB of 1866MHz LPDDR3 onboard memory and 2014 is 8GB of 1600MHz DDR3L onboard memory
http://www.apple.com/ca/shop/product/FGX92LL/A/Refurbished-133-inch-MacBook-Pro- 28GHz-Dual-core-Intel-i5-with-Retina-Dis…
http://www.apple.com/ca/shop/product/FF840LL/A/refurbished-133-inch-macbook-pro- 27ghz-dual-core-intel-i5-with-retina-display