what was the dose of insulin that during their first hospital encounter patient 66015 was last prescribed?
select prescriptions.dose_val_rx from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 66015 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and prescriptions.drug = 'insulin' order by prescriptions.startdate desc limit 1