I'm debating this same question, but coming at it from a little different perspective. I have a 15" 2015 MBP and a 13" 2017 MBP. The 15" is my work horse and I use it with Final Cut, Lightroom and Pixelmator Pro. My favorite computer however, is the 13" MBP. Whenever I'm at home reading emails, surfing the net, or watching Youtube videos it's my go to machine. I also choose the 13" when I have to travel, although I don't really travel all that much. I'm planning on upgrading one of these machines, but I'm having a tough time figuring out which one to buy. The 8 core 15" MBP would be a great upgrade for my work, but I'm wondering if the new quad core 13" might encourage me to use it more for photo and video projects.
One other consideration for me, is that since the 2019 13" isn't that much faster than the 2018, if I decide to upgrade the 13" machine I could buy one of the discounted 2018 models.
I’d say get the new 15” and keep the 2017 13” for web / emails. If you can afford it of course.