I have heard that some people take as little as 15 minutes to pray 5 decades of the rosary. In order for this to be possible you have to say it very fast, like with no pauses at all.

I have timed myself and if I pray it at a "normal" or "regular" pace, not rushed and not slow either, and with no interruptions, I take 4 minutes and 30 seconds on average for 1 decade, and I only enunciate the mystery, say 1 Pater, 10 Aves, Gloria and the Fatima prayer, and that's it. I don't add anything else to each decade. I know some people may pray it according to the various methods of St. Louis Montfort, and that makes it even longer.

Even if I were to round it to 4 minutes for each decade, that would still be, at the very least, 20 minutes for each mystery.

So how can some people take as little as 15 minutes? Although I don't use any of the methods of St. Louis, since they are counselled and not commanded, he did say it's bad to pray it fast and without any pauses, and I don't think that was a mere counsel.

If you have the time then take a long as you like.

If you don't then 15 minutes and no "pauses" is better than nothing.

Plenty of families find it a struggle to find a common 15 minutes every day.  Between parent evenings, supervising homework, cooking a meal, washing up, sorting bills, getting kids washed and to bed 15 mins plus 5 either side to set up, call people from around the house, pack away and get on with something else 15 mins is not always easy to find.

I try not to let perfect be the enemy of good.

Are you saying that you don't even have at least 20 min for 5 decades of the Rosary every day, or are you speaking for other people?

He who prays the fastest is not necessarily the most holy. If there is a person or a family that finds it a struggle to be able to pray five decades without feeling they have to rush through then maybe they should just pray one decade and take the time to pray it well.