My previous shelties lasted 2yrs (poisoned), 10 yrs (testicular cancer) and 15yrs (heart). I fed them crap back in the day so I'd hope my current shelties live longer. That said, Deska at 7yrs is struggling with arthritis so I think I'll be lucky if he manages to 10yrs. Tully on the other hand, well I've told the vet her new hip has to last at least 10yrs, and she's 6.
I had one sheltie live from 1992 to 2010 eating pedigree (a low rated food) with arthritis the last 7 years of her life; hopefully your fur babies will do as well....