SQL performance issue over system catalog

Any idea why following SQL takes forever to run first time?

Trying to use catalog tables instead of doing DSPOBJD. It looks like old
way of using DSPOBJD to output the file and then compare works faster...

With SourceStats (ObjectName, ObjectType, ObjectAttr) as
(Select objname, objtype,objattribute
from table (QSYS2.OBJECT_STATISTICS('PRODLIB', '*ALL')) as src),
TargetStats (ObjectName, ObjectType, ObjectAttr) as
(Select objname, objtype , objattribute
from table (QSYS2.OBJECT_STATISTICS('TESTLIB', '*ALL')) as tgt)
Select s.ObjectName, s.ObjectType , s.objectAttr
from SourceStats as s
exception join TargetStats as t
on t.ObjectName = s.ObjectName