Macbook Pro 15" vs 13" - Performance vs portability
Here's the way it goes in our household:

I own the 15" Model you describe above (albeit a slightly earlier version with the GTX750M GFX card) and my other half has the 13" you describe above (again, albeit 6 months old at this point)

Now, she does a lot of graphical work on it in Adobe CC - Photoshop, Illustrator, InDesign, etc - much the same as you want to. She says it never skips a beat for her, even when she's running it on external displays in the office and driving the graphics side of things hard. She sometimes gets frustrated with the lack of screen real estate compared to mine (when she does use it) but it's generally not a problem for her. The battery also performs a bit better, which helps if you're on the move a lot. Sure, a bit of extra power would help her but the portability and price trade offs aren't worth it.

Based on what you've said, I'd recommend the 13". It's plenty powerful for what you want, but I would use the left over cash to buy a couple of nice 24" external displays if you have the space to set up a small office. I love having 3 displays running (1 on the MacBook + 2 external.) Better on so many levels!

Another note - it used to be possible to upgrade MacBooks (more RAM, swap out the HDD for an SSD, etc) so I used to recommend buying less and adding to it when you need it. Can't do that anymore, so buy as high spec as you can afford.