I just learned that one of my favorite ways to pass the time in a hotel gym has been given a catchy name and a celebrity endorsement. Its the 15-15-15 workout, and it will give you a good 45-minute cardio session even if you cannot stand doing anything for 45 minutes straight.What is the 15-15-15 workout?The 15-15-15 is a simple idea: You just do 15 minutes each on three different cardio machines. Like so:15 minutes on a spin bike15 minutes on the elliptical15 minutes on a treadmillIve often done a version of this when Im at one of those sad hotel gyms with few or no weights, just cardio machines. Theres usually a treadmill, an elliptical, and/or a bike, so Ill do a few minutes on each. The 15-15-15 version will give you a 45-minute workout.Where did the 15-15-15 workout come from?As far as I can tell, its origin is in one brief quote from an interview that Jennifer Aniston gave to In Style magazine in 2021. She said that, after taking time off for an injury, I was missing that kind of sweat when you just go for it. Im going back to my 15-15-15, which is a 15-minute spin, elliptical, run.Why the 15-15-15 is perfect if cardio bores youIf you get bored on cardio machines, a 45-minute workout is a pretty big ask. But 15? You could manage 15, Im sure. Thats just a five-minute warmup, five minutes of solid work in the middle, and then for the last five minutes youre on the home stretch. (Mentally breaking up workouts like this helps my brain, even if I'm doing the exact thing for all 15 minutes.) Then hop off that machine, choose another, and repeat. Three of those mini workouts and youve done 45 minutes for the day.Feel free to adjust the timing as needed; you could do a 10-10-10 for a 30-minute workout.How hard should the 15-15-15 workout be?Theres no wrong answer to this question. The 15-15-15 would be a great way to get in a zone 2 cardio workout, going at an easy conversational pace for all three segments. Some people find zone 2 work to be easy and fun, and theyll watch a video or chat with a friend while doing it.But some of us get bored more easily, and breaking each mini-workout into intervals can make it a lot more engaging. Try this:Warm up for three minutes at an easy pace.Go hard for one minute, then recover with very easy activity for one minute.Repeat those intervals five more times, for a total of six hard and six recovery minutes.Thats three minutes of warming up, and 12 minutes of alternating intervals, ending with an easy minute. You can do this mini routine on each machine in turn, or only on some of themperhaps the first and the last, while challenging yourself to hold a steady state on the middle machine.Can you do the 15-15-15 on different machines, or in a different order?You sure can! Theres nothing magic about the order of bike, elliptical, run. You can move them around. You can also swap in different equipmenthow about stair stepper, bike, rowing machine?Or, heck, bounce between the bike and the treadmill if you only have those two machines available. (Hello, again, to very small hotel gyms.) The 15-15-15 isnt so much a workout as it is a structure that you can fill in with any workouts you desire, so feel free to get creative.