I speak very highly about optics and their importance but although optics will increase your speed, accuracy, and distance, you must be proficient with your iron sights! It is highly recommended that you master the iron sights before you move on to optics.
The AR-15’s Ghost ring sights are the fastest of all aperture sights and the preferred sight of combat rifles. It is fairly simple to use and it obscures very little of the target when compared to most other front sights. Ghost rings get their name by the way the rear ring “ghosts” out of focus when using the sights. So, your focus is on the front sight.
Optics can and will fail at the worst possible time. Even with an excellent red dot sight and the ability to use it, you have to be able to defend yourself with well-aimed shots in the event of a sight malfunction. Optics can fail. Batteries can fail. Your optic could be dropped, shot, etc…
I have found that the fastest and most accurate way to shoot the AR-15 is to keep your “nose to the charging handle”. You may have heard this phrase on gun boards or elsewhere like in carbine classes, military or LE training, etc. but I have found this to be the preferred method for quick and accurate shooting with the AR-15.
Keep in mind that your nose doesn’t necessarily have to be touching the charging handle, but you do want it right up close to there and you want to try to get as good of a consistent cheek weld as possible. By keeping you nose to the charging handle, you can let the “ghost ring” disappear like they were designed to and keep your focus on the front sight and your target.
This is one of the reasons I do not like a very long stock on my AR-15’s even though I am 6’2”. In contrast, if you keep your face back and away from the ghost ring you will undoubtedly be less accurate and/or quick. It’s the best way to keep a consistent cheek weld. I’ve also noticed that it allows me to control the weapon better as well.