DBCA includes creation of files so the first bet is to check slow IO/storage issues, you also say create table taking time this again points to IO slowness.
If you have OSWatcher installed please check IOSTAT output, and see if there are any slow performing disks.
Still other ways to find the issue:
-- Generate AWR report covering the table creation duration.
-- Enable 10046 event tracing and then create table
-- Or simply issue the create table statement and query v$active_session_history table where the session spending time during creation of table.
Let me know if you have any questions.
Describe the Interconnect infrastructure.
Describe the shared cluster storage architecture.
My knee jerk reaction is that it is partly due to a shoddy Interconnect, and mostly due to a horribly slow and inefficient shared storage.