PostgreSQL is definitely a boost to performance, especially if you offload the DB to a dedicated server (depending on load, can even be a cluster)
Nevertheless, it probably has much to do with how it's deployed and how many proxies are in front of it, and/or VPN. If you have large numbers of containers and small CPU/low memory hardware, and either running everything on one machine or have some other limitations, it'll be slow.
Admittedly, I'm not very familiar with the codebase, but I feel Apache isn't improving the speed either. Not exactly sure how PHP is nowadays with concurrency and async, but generally a microservice type architecture is nice because you can add more workers/instances wherever a bottleneck emerges.