When we check if the user can see the list of participants, in old Moodle versions we use the moodle_enrol_get_enrolled_users that don't support pagination

In large courses with lots of users this is very very slow, we should try to use the additional parameters of that function to filter the resulset because that what really interest us is to receive an exception if we cannot see users:

get_enrolled_users($courseid, $withcapability = null, $groupid = null, $onlyactive = false) {