players from how many teams have participated in the 2015 thai division 2 league north eastern region ?
SELECT DISTINCT COUNT attr_open var_uri attr_close where brack_open var_x dbp_league dbr_2015_Thai_Division_2_League_North_Eastern_Region sep_dot var_x dbo_team var_uri sep_dot var_uri a dbo_SportsTeam brack_close