Adding onto Sravanthi’s comment, that Bahmni is composed of many components & services - while they might add up taking more resources than a single monolith, the advantages are reuse of existing open source softwares, ease of development, maintenance, deployment to name a few. If you run just the EMR, you will see noticeable difference. One of our clients use a cloud hosted Bahmni (only EMR), and they serve 100s of concurrent users.
Like Sravanthi mentioned, there are lots of background threads that are continuously working for interaction between systems. For example, if you would reduce the polling intervals of some of the scheduler, you might find that less resources are consumed. We run multiple databases (MySQL & Postgres), because of subsystems dependence; if we could move to one single dbms, we would. Maybe someday we will use just Postgres.
Keeping a balance between modularity, composition and optimization is hard, and Bahmni still has a long way to go.