I wouldn't worry about 5 minutes, 15 is a bit iffy but if you can't fall asleep before half an hour of going to bed then you're either not tired enough or over stimulated.
The thing about the sleep cycles is that if you wake up in the delta sleep phase of the cycle you will feel very tried and groggy for some time after you wake up while you brain waves revert from delta waves to alpha waves. The recommendation to get entire sleep cycles is so that you can wake up in the phase of the sleep cycle (end or beginning of the next one) where your brain is in an almost wakeful state.
My suggestion would be that you adjust you waking time for that night and then examine your pre bedtime routine and perhaps do less stimulating things and start dimming lights half an hour before bed.
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