Survivors of Oceanic Airlines Flight 815?
On the island:
1)Jack Shephard 2)Kate Austen 3)James "Sawyer" Ford 4)Hugo "Hurley" Reyes 5)Sayid Jarrah 6)Jin-Soo Kwon 7)Sun-Hwa Kwon 8)Claire Littleton 9)Rose Nadler 10)Bernard Nadler 11)Cindy Chandler
and Zach and Emma and the rest of the tail section survivors who were kidnapped. (Assuming Rose and Bernard time travelled with the others at the end of season 5, which you assume they would, but not yet confirmed)
Off the island:
Walt Lloyd Aaron Littleton
Then there's the unknown number of survivors of Ajira Airways Flight 316, most prominently Frank Lapidus and Ilana. And still there from the Kahana freighter, Miles Straume.
But if i'm interpreting your question right about being major 815 characters, the answer would be 11 major named characters plus change. Most of the 815 survivors died in the flaming arrow attack.