Among the complaints received in year 2015, what is total number of complaints timely response and closed with an explanation?
in year 2015 refers to Date received LIKE '2015%'; timely response refers to Timely response?" = 'Yes'; closed with an explanation refers to Company response to consumer = 'Closed with explanation'
SELECT COUNT(T1.`Complaint ID`) FROM callcenterlogs AS T1 INNER JOIN events AS T2 ON T1.`Complaint ID` = T2.`Complaint ID` WHERE strftime('%Y', T1.`Date received`) = '2015' AND T2.`Timely response?` = 'Yes' AND T2.`Company response to consumer` = 'Closed with explanation'