instruction: when was the first time on 06/26/2100 patient 015-15167's sao2 was greater than 99.0?
response: SELECT vitalperiodic.observationtime FROM vitalperiodic WHERE vitalperiodic.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '015-15167')) AND vitalperiodic.sao2 > 99.0 AND NOT vitalperiodic.sao2 IS NULL AND STRFTIME('%y-%m-%d', vitalperiodic.observationtime) = '2100-06-26' ORDER BY vitalperiodic.observationtime LIMIT 1