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When adding another entity to a project the wizard reloads the database schema again although there is a cached version. Depending on the size of the schema this can be painfully long...
When invoked for the second time the wizard should find the dbschema file generated by the previous invocation and select it in the Database Schema combo box. Does that not happen for you?
It is by design. In the same IDE session, it remembers what you just did. If you restart the IDE, the wizard searchs for the dbschema files first. Also see issue 74113