After owning both the 14 and the 15 pannys I'm selling the 15 1.7 and keeping the 14. I never reach for the 15 instead of the 14; I find the rendering of the 14 quite nice and the incredibly compact size always wins out when picking up my smaller m43 cameras. My use case has dramatically changed for m43 and now I'm reaching for it for one of two reasons; a lot of reach in a relatively compact package (12-100 and 100-400) or very compact to compact to keep a better option than a phone on me (ep5, epl-9, gx9, 14, 12-32, or Oly 45 1.8). Lenses like my 15 are neither compact enough nor optically superior enough (unlike the Oly pro primes which very much are worth their weight and size penalty) to warrant me using it.
I never gelled with the 15 the same way I have the 14; I have thousands of images made with the 14 and a few hundred with the 15. I'm not using m43 generally as much as I have in the past, but I'm particularly not using the 15 at all.
Which is why you'll find it currently listed in buy/sell/trade section and not my 14.
Also haven't had any issues with focusing speed with my 14. Is the 15 quicker? Maybe, but my luck in poorly lit indoor spaces was no better with the 15 than the 14 so there's that. In good lighting it's been six in one hand, half a dozen in the other between the two of them.
Dennis