The short answer is that 155° (for breast meat) is moist and still has a good texture. The USDA recommends cooking chicken to 165° because it's easy to remember, and at 165° bacteria has been eliminated, and pasteurization has occurred.Looks amazing! I'm genuinely curious on why you SV at 155 vs 165?
The long answer is sous vide uses a combination of temperature and time to achieve pasteurization. So... Chicken cooked to 155°, then held at 155° for 1-minute will be pasteurized. Chicken cooked to 152° and held for 2-minutes will be pasteurized. This method of temperature and time is called a 7-log 10 reduction, and is approved by the USDA. Restaurants use this to some degree. This article explains this using baked chicken, but sous vide gives me better temperature control.
Juicy Baked Chicken Breasts | The Critical Pull Temperature
Don't settle for dry chicken. Learn the exact internal temperature for succulent baked breasts and the science of moisture retention.