CREATE TABLE table_76981 ("Poll source" TEXT, "Dates administered" TEXT, "Jim DeMint  ( R ) " TEXT, "Alvin Greene  ( D ) " TEXT, "Tom Clements  ( G ) " TEXT, "Other" TEXT, "Undecided" TEXT)

Which poll source had an other of 15%?
SELECT "Poll source" FROM table_76981 WHERE "Other" = '15%'
SELECT "Poll source" FROM "table_76981" WHERE "Other" = '15%'