One week ago I received my maxxed out 13''. I am blown away by display quality and build. But. I am also negatively blown away by 3-4 hours of battery life at medium-intensive work and 1-2 hours at intensive work. And by a constant lagging UI. I am taking it to the Apple Store in a couple of days, to at least get the screen replaced for a minor yellow tint along the whole left edge of the screen, but I am now thinking whether I should replace it with a discrete GPU 15''. My concern is the size. 13'' is just right for me. Bigger than that I would't feel comfortable carrying it around. So I feel like I am in an impossible situation. Stay 13'' and suffer? Or go 15'' and get used to size? Any advice is much appreciated.