Among universities that score below 80 in 2015, what is the percentage of international students?
score below 80 refers to score < 80; in 2015 refers to year 2015; percentage of international students refers to DIVIDE(SUM(DIVIDE(MULTIPLY(num_students, pct_international_students), 100)), SUM(num_students))
SELECT SUM(CAST(T1.num_students * T1.pct_international_students AS REAL) / 100) / COUNT(*) * 100 FROM university_year AS T1 INNER JOIN university_ranking_year AS T2 ON T1.university_id = T2.university_id WHERE T2.score < 80 AND T1.year = 2015