###HUMAN: when was the first time that patient 015-91239 had the maximum value of respiration on the current icu visit?, ###ASSISTANT: 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 = '015-91239') AND patient.unitdischargetime IS NULL) AND NOT vitalperiodic.respiration IS NULL ORDER BY vitalperiodic.respiration DESC, vitalperiodic.observationtime LIMIT 1