I made a video of my challenge runs. You can find my chocobo's build at the time linked in this video:
https://youtu.be/YANRDLKJeCE?t=260

And you can find my challenge 15 race here:
https://youtu.be/LHZJhW8pEP4?t=210

I've done the last challenge a few more times afterwards and I have a 95% ish win rate with this build.