Long Parse Time for a big Statement

At one customer site we see generated statements, actually reports. The parsetime for such a statement is over an hour, if it finishes at all. It is possible we see "ORA-04031:" when we run out of memory in the shared pool.
How big these statements are is hard to tell, since it depends on formatting. With sql developer formatting i get in one typical example > 130000 lines.
The statements are constructed relatively simple. It seems to be a kind of change report where columns from different tables are retrieved.
At the beginning is a big case statement where a meaningful name is generated for a value followed by this values. I counted 7400 case entries as per statement in one case.
I addition we have  a number of big inlists. All this is running against a union view of 55 Tables. In other words: If i want to stress the parser I would construct a statement exactly like this.
However, one hour seems to be a unrealistically long parse time. Even though that statement needs to be rewritten, but this will take time. I want to know if there is any quick fix like increasing the shared pool a lot. (Which I can't test unfortunately any time soon due lack of memory). Any ideas how to speed up the parse time?

Database version is 19.7. Shared Pool size is 20GB

Thanks

Lothar

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