Joining v$session direclty to v$lock seem slow.
Doing and inline view seems to fix it.

SQL> @txl

USERNAME          SID TY        ID1        ID2      LMODE    REQUEST      CTIME
---------- ---------- -- ---------- ---------- ---------- ---------- ----------
SYS                59 TM     569189          0          3          0        661
SYS                59 TX     655382      63226          0          6        661
SYS               176 TX     655382      63226          6          0        673
SYS               176 TM     569189          0          3          0        673