I don't share the same opinion as some of these memory related parameters might have a big impact
on the resource usage of the DB instance. E.g. increasing heap dump per user from 12K to 64K would
increase memory usage for 500 concurrent users from 6GB to 32GB. So the DBA should be very careful changing these values.
But my question was more related to why it changed in 15.7 as the very same statement runs fine in 15.5 with 12K heap.