Slow query - why?

Hey guys, I’ve got following problem:

I have documents: {title → string, key_words: array, organisation → string, article → string).

my atlas search index (name is ‘only_text’) is:

{
  "mappings": {
    "dynamic": false,
    "fields": {
      "key_words": {
        "analyzer": "lucene.standard",
        "type": "string"
      },
      "organisation": {
        "analyzer": "lucene.standard",
        "type": "string"
      },
      "title": {
        "analyzer": "lucene.standard",
        "type": "string"
      }
    }
  }
}

my NodejS query is:

await dbo.collection('jobs').aggregate([

                {

                  '$search': {

                          index: 'only_text',

                          text: {

                            "query": "referent",

                            "path": "title"

                          }

                            

                  }

                  

                }, 

              ]).toArray((err, result) => {

                if (err) throw err; 

                res.status(200).json(result)     

           

            })

on my first query, its VERY slow, up to 12 seconds… My database only consists of 250 documents… what do I wrong? Thanks