The documentation uses 16 & 8 as example values for the ingestionBurstSize & ingestionRate. The default values in Openshift 4.14 are 20 & 15. 

apiVersion: loki.grafana.com/v1
kind: LokiStack
metadata:
  name: logging-loki
  namespace: openshift-logging
spec:
  limits:
    global:
      ingestion:
        ingestionBurstSize: 16 
        ingestionRate: 8

OpenShift configmap logging-loki-config in namespace openshift-logging:
...
limits_config:
  ingestion_rate_strategy: global
  ingestion_rate_mb: 15
  ingestion_burst_size_mb: 20
...

The documentation suggest