The NG/G16 to which you refer is actually an NG/G13 but the weights are similar. The max "book" axle load either is about 15400lbs. The NG15 2-8-2 is similar for the locomotive but the tender, fully loaded, maxes out at about 17800lbs loaded.
Required rail weight depends upon many factors including axle loading. Others are sleeper spacing, speed of trains etc.
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