It's 'normal' for the 1st or 2nd call to this take awhile. However, after that it should be in the neighborhood 1 sec calls.
I wouldn't say it's normal to take 15 minutes though.
Are there any system-level Oracle tables containing database metadata which might need attention (or more likely, the indexes on various tables)?
Your DBA can generate/collect statistics on the data dictionary and fixed objects.
For convenience, here is a link (although it is for Oracle 12.2) to the dbms_stats package methods gather_dictionary_stats and gather_fixed_object_stats:
Ran DBMS_STATS.GATHER_DATABASE_STATS(), and it seemed to work! (I just wasn't aware of the different statistics types.)