Can we enable trace to overall instance

Hi Experts,

I would like to know,what all sql statements and how many times each statement executed in 15 minutes from the point i enable the trace.I can then do tkprof and view the results.Please let us know if there is any method through which i can achive this.

I am doing this but the resultant tkprof is empty

as sysdba

SQL> alter session set events '10046 trace name context forever,level 12';

Session altered.

Wait for 15 minutes

and then disable trace