Kibana 8.12 transform process is too slow

Elastic Stack Elasticsearch
1

Every hour text files ar ingested to update the index. I have the following code of a process that transforms the data to seconds.

  "version": "10.0.0",
  "create_time": 1714766696988,
  "source": {
    "index": [
      "trx_hours_new"
    ],
    "query": {
      "bool": {
        "must": [
          {
            "range": {
              "@timestamp": {
                "gte": "now-6h"
              }
            }
          }
        ]
      }
    }
  },
  "dest": {
    "index": "trx_hours_history_segundos_sp"
  },
  "frequency": "20m",
  "sync": {
    "time": {
      "field": "@timestamp",
      "delay": "60s"
    }
  },
  "pivot": {
    "group_by": {
      "@timestamp": {
        "date_histogram": {
          "field": "@timestamp",
          "calendar_interval": "1s",
          "missing_bucket": true
        }
      },
      "nodo": {
        "terms": {
          "field": "nodo"
        }
      },
      "sp": {
        "terms": {
          "field": "sp"
        }
      }
    },
    "aggregations": {
      "segundo_prom": {
        "avg": {
          "field": "tiempo"
        }
      },
      "cant_trn_seg": {
        "value_count": {
          "field": "trn"
        }
      }
    }
  },
  "description": "trx_hours_hist_seg_sp",
  "settings": {
    "max_page_search_size": 19000
  }
}

1 hour of data could has 1.2 millions of documents and can take more than 1 hours to execute.
Any advice ?
Thanks in advance.