I've not prepared a roast this way, so I don't have a great answer for your question, but my go-to is Kenji Lopez-Alt on seriouseats (along with someone he recommended whose name I can't remember). It seems like there are two styles of sousvide recipe: cook to the desired temperature and stop, or cook until pasteurized. For example the 129.5 should reach 129.5 throughout, but will have spent more than the recommended time in the food safety "danger zone". I suspect the longer cooking time version is designed to cook and pasteurize.
I've been happy with the advice I've gotten from ChefSteps: https://www.chefsteps.com/activities/win-the-holidays-with-herb-crusted-sous-vide-prime-rib-rib-roast
I have found absolutely no consistency in time and temperature for sous vide recipes--they're all over the place. Respected chefs and cooking teachers giving wildly different advice, just as you have found. I find this bizarre since this method is supposed to be so "precise." Based on my own experience, I think 15 hours @ 135 degrees is going to get you something a lot closer to medium-well than medium-rare.
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