Cleaning guns is no different than cleaning your car, clothes, house, or anything else. You can do it quick and dirty, and call it "good enough", or else you can take your time and do it properly. There are no "rules" except the ones you make and choose to live with.
It's no secret a semi auto, any semi auto, requires more time to clean than say a bolt action. The direct impingement AR-15 more so because it craps where it eats. To do it correctly takes time. There isn't any way around this. So in the end it all boils down to what satisfies you. AR-15 rifles cost a lot of money in relationship to many other guns. Personally, I feel any gun, regardless of cost, deserves to be as clean and attended to as I can make it. When dealing with AR-15 rifles that takes me far longer than 15 minutes.