Fluentd mongo output slow

Hello is there anything i can do to improve mongosb speed. I am doing a side project now and want to push data from fluentd to monodb. I have 4 shards with no replication + 3 mongos servers. All 7 pods are allowed to consume 16 cpu and 128GB but they are not it’s about 4 cpu and 64GB of RAM. Biggest ingestion speed i saw was about 15k/s . I read about shard keys and added hashed shard keys per collections but still no speed improvement for ingestion. How to start troubleshoot the problem and how/ what else i can tune?

In mongo i see these warnings “slow query” with mesage “Insert…” a bit bizarre

{
  "t": {
    "$date": "2023-02-17T12:39:37.389+00:00"
  },
  "s": "I",
  "c": "COMMAND",
  "id": 51803,
  "ctx": "conn206926",
  "msg": "Slow query",
  "attr": {
    "type": "command",
    "ns": "datalake.dns",
    "command": {
      "insert": "dns",
      "$db": "datalake",
      "ordered": true,
      "$clusterTime": {
        "clusterTime": {
          "$timestamp": {
            "t": 1676637357,
            "i": 7390
          }
        },
        "signature": {
          "hash": {
            "$binary": {
              "base64": "K6OBJjwSuhR7YiIgMz+GlmwN8lY=",
              "subType": "0"
            }
          },
          "keyId": 7198499255500144644
        }
      },
      "txnNumber": 17,
      "lsid": {
        "id": {
          "$uuid": "ebfd21c2-5969-4d85-b0ae-d7c91c63bf99"
        }
      }
    },
    "nShards": 4,
    "ninserted": 7805,
    "numYields": 0,
    "reslen": 170,
    "readConcern": {
      "level": "local",
      "provenance": "implicitDefault"
    },
    "remote": "192.168.67.196:53746",
    "protocol": "op_msg",
    "durationMillis": 194248
  }
}