Oracle 18c much slower compared to 11g

Needed to upgrade from Oracle 11g XE to Oracle 18c XE for licensing reasons. We run Oracle in containers for use in integration tests.

However after upgrading from 11g XE to 18c XE queries are significantly slower.
This is mostly the initial queries for each table. Subsequent queries are comparable to 11g.

tldr; Is there a way to "heat up" the 18g in some way to make each initial query also run fast?

Source: Docker Questions