Deleting rule project can be very slow in Decision Center, even when there's only few rules in the project
Deleting a rule project in Decision Center could be very slow, and even timeout, when there are only a reasonable amount of rules in the project. The problem doesn't happen to projects that are recently published to Decision Center
This is because Decision Center has a feature to keep all the history versions of rule artifacts in the database, which will allow you to explore an history version, and/or restore it at any time. This kind of history data will stay in database until you erase the entire project.
As a side effect, the size of Decision Center database will keep growing when you do any update to the rule artifacts. Thus it will be very time-consuming to erase a rule project with huge history, even if there are not many active rules.
To avoid this problem, you can periodically use the archiving tool to archive/remove old records in Decision Center database. Refer to documentation at Decision Center > Administering Decision Center > Archiving the Decision Center database
You can also find a step-by-step example of how to use the archiving tool in this blog entry