We just updated iLearn to Moodle 2.6.1 last week and some teachers were complaining about slow load times when trying to use Quickgrading when looking at Assignments. The issue stems from the way Moodle wants to build the table with all the student data.
It is a bug with Moodle 2.6.
As soon as a fix is available we will apply it. Thank you for your patience.