do you like a higher res? 15" retina scaled comes in at 1900x1200, which is perfect imo. i find less than 1200 vertical too short, but that's just me. 13" is 1600x1050, which is barely taller than a mba.
I think this is the key difference. At next-to-highest resolution, the 15" gives you a heck of a lot of workspace readable even with these old eyes (with reading glasses ;-).