This is correct:

SQL> select round((to_date('01/01/01 01:15:00','mm/dd/yy hh24:mi:ss')-to_date('01/01/01 01:00:00','mm/dd/yy hh24:mi:ss'))*1440) from dual;

ROUND((TO_DATE('01/01/0101:15:00','MM/DD/YYHH24:MI:SS')-TO_DATE('01/01/0101:00:00','MM/DD/YYHH24:MI:
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15