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I assume you are talking about layer hens. They generally need around 16% or 17% protein, a little more in the summer, less in the winter when they are eating more feed anyways. They'll get by on 15%, but if they are young, high production layers it may fall a little short as a sole ration and production will suffer. 15% would be a better fit for older hens who are no longer growing and are laying more intermittently.
As far as organic vs non-organic... It really depends upon your personal convictions. It's doubtful that you will see any difference in performance or health of your hens. The draw to organic is that some feel it is more "environmentally friendly", as organic grains are raised without synthetic herbicides, pesticides, or fertilizers. There are some that feel that these chemicals can be passed on through the food chain (from grain, to hen, to egg, to you) so they opt for the organic feed.
Which ingredients to look for? That opens up a whole 'nother can of worms. You can do some reading here and come up with 100 different opinions. Generally, if it is sold as a layer ration for chickens your birds will do fine on it as it will be formulated to provide the basic nutrition that a layer hen needs.