Setting spec.apicast.productionSpec.logLevel or spec.apicast.stagingSpec.logLevel on the APIManager resource is expected to update the log level on the corresponding deployment, see stagingSpec, productionSpec.

In 2.15 setting these fields resulted in an immediate change of the corresponding Deployments - setting the APICAST_LOG_LEVEL enviornment variable.
Moreover, in 2.15 setting this variable directly on the Deployment was not possible, it was immediately removed.

In 2.16 it is possible to set the env var manually on the deployment, but setting/unsetting logLevel on APIManager does not add/change/unset the env var.