When to start layer? 15 weeks and still on chick feed.

Previously used H and H old fashioned layer non GMO for my production red. Let her hatch and raise some chicks, and they've all been eating chick feed since birth 15 weeks ago. Stay with chick feed until 20 weeks? Recommendations on brand of layer feed? Previously disappointed with the H and H old fashioned layer feed as some bags were mostly all pulverized powder and and other bags were good hardy grains and little powder