From Golf Digest interview with USGA technical chief a brief explanation of the "rollback" amount:
Can you explain where the 14-15 yards figure is from? We've seen some simulations that show more like 20-25 yards.
SPITZER: Going from 120 to 127 [the proposed new swing speed for the golf ball test for elite competitions] is a little more than a 5.8 percent increase. 20-25 yards would be more like 6.3-7.9 percent, which doesn’t agree with our research. For players with swing speeds that are near or above where we currently test, we estimate the effect to be 18 yards (which is about the same 5.8 percent). Remember, that you need to consider that golf balls have diminishing returns the harder that they are struck because the coefficient of restitution decreases at higher speeds [Note: Coefficient of Restitution or COR usually refers to the springiness of driver faces, but it also applies to the resilience of golf balls. A super ball has a high COR, a Nerf ball has a low COR.] Players closer to the average swing speed (approximately 115 miles per hour) lose slightly less; 14-15 yards.
This is pretty rudimentary arithmetic. We won't really know how the MLR impacts different swing speeds until some prototype balls are developed and tested and that comply with the new ODS testing protocol and standard.
The USGA has an algorithm that estimates distance based on measurements gathered in their ITR to determine if balls comply with the ODS. Flightscope has a similar algorithm that produces the following results for the tour average speed, 120 mph and 127 mph respectively - 292.5, 306.1 and 323.4 yards. The USGA algorithm would presumably show 317 yards for the current balls at 120 mph. Perhaps their algorithm assumes harder ground and more rollout. In any event the Flightscope shows a 17 yard difference between the 120 and 127 mph swing speeds - in the same ballpark as the USGA's numbers.
Anyway, all the wailing and gnashing of teeth seems a little premature and a lot over the top. The new ball may be shorter for the elite players but I doubt that it would perform substantially different in any other way. The USGA has dipped it's toe in the distance rollback water and the water is hot, albeit heated for different reasons from different pro and anti rollback and bifurcation camps.