My 2015 PR4s came off the bike in May with 12,000 miles on them. They could have easily done another few thousand, but we were heading out on a 6,600 mile trip so they were replaced with a new set of PR4s.
I once killed a precious day and a half of vacation time hunting down new tires to make it home. Now I leave home with fresh tires if there's any doubt of my old ones lasting the whole trip.
The 2015 take-offs are tucked away as back-ups "just in case."