There have been some shops that have had issues with summarization and pruning of TDW data taking an inordinate amount of time. When you are summarizing or pruning millions of rows of data, this may take some time.
It's always useful to keep in mind that TDW is, fundamentally, a database. That means you may need the usual tuning and tweaks needed for any database. As I've mentioned in prior posts, TDW has the potential to gather quite a bit of data, and become quite large, so database tuning may become a factor.
Here's a link for some suggestions for DB2: