Among the universities in Australia, how many of them have more than 15000 students in 2011?
in 2011 refers to year 2011; have more than 15000 students refers to num_students > 15000; in Australia refers to country_name = 'Australia';
SELECT COUNT(*) FROM university AS T1 INNER JOIN university_year AS T2 ON T1.id = T2.university_id INNER JOIN country AS T3 ON T3.id = T1.country_id WHERE T3.country_name = 'Australia' AND T2.year = 2011 AND T2.num_students > 15000