What is the 'season joined league' for the club that had 15 seasons at this level?
CREATE TABLE table_name_54 (
    season_joined_league VARCHAR,
    seasons_at_this_level VARCHAR
)
SELECT season_joined_league FROM table_name_54 WHERE seasons_at_this_level = "15 seasons"
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: What is the 'season joined league' for the club that had 15 seasons at this level? ### Input: CREATE TABLE table_name_54 (
    season_joined_league VARCHAR,
    seasons_at_this_level VARCHAR
) ### Response: SELECT season_joined_league FROM table_name_54 WHERE seasons_at_this_level = "15 seasons"