I always thought just the opposite.....tho some layer feeds are 18% and can be higher, but it's rare.Layer feed is higher protein than grower. Granted, it's only a tiny bit higher, but... that may have a bit enough of an effect to make a difference. My birds always lay sooner than those of my friends, though they are same age and get feed from same source. My flock gets fermented feed, which gives them a nutritional advantage.
Gotta read the labels.