Disk Utility Having a Tough Time today = MULTIPLE Spinning Beach Ball[s] of Doom

I confess to getting very neglectful with our 2014 MacBook Pro, as in never using Disk Utility on its hard drive. Its operating speed finally became noticeably slow, so I dusted off its trusty Disk Utility/First Aid program. At first DU/FA's processing appeared "normal" enough, but then the Spinning Beach Ball of Doom appeared. I went to another laptop and discovered pressing "OPTION + COMMAND + ESCAPE" at the same time opened Force Quit, allowing me to quit "Disk Utility (not responding)." That made the SBBD disappear, and Disk Utility as well. Being a bit stubborn, as well as neglectful, I got back on the horse and gave Disk Utility/First Aid another opportunity to clean up our MacBook Pro's hard drive. DU/FA would run for about five minutes then the screen saver would appear. When I'd wake it up the SBBD was there again. I repeated this exercise multiple times, each time "reporting" the DU/FA's shutdown to Apple, just because they seemed to like that kind of stuff.

Also note: after I'd get by the SBBD this is the message that would appear in the Disk Utility/First Aid program:

"error: Cross Check: FSroot tree reference extent (0 x 2794b8c +25) which is not present in the ExtentRef tree."

But the (number) always changed slightly, which I interpreted as some form of slow progress, and continued to relaunch Disk Utility/First Aid. When one of those numbers finally repeated, the illusion of "progress" vanished.

Final note, our laptop's HD is 480GB. Of that 272GB are "Used," 21 GB are "Other Volumes" and 186GB are "Free." In retrospect, I am now wondering whether this going nowhere DU/FA exercise means we have outgrown this otherwise wonderful laptop's hard drive. The impossibility of successfully running Disk Utility may be the least of the problems on our horizon.

Any useful tips/observations from the Apple community are always greatly appreciated.