I currently have a query using mongodb3.4, that needs to be paged. Paging needs to return the total number and number of pages.
but that"s the problem. Paging queries are fast, but counting is slow

count statement is as follows:

db.message.find(
    {
        "field_1":"ajian",
        "field_2":{ "$exists": true },
        "field_3":{ "$exists": true },
        "field_4":{ "$exists": true },
        "field_5":{"$regex":value1},
        "field_6":{"$regex":value2}
    }
).count()

it takes 2.5 seconds to return the result!
the info results of my explain are as follows:

{
    "queryPlanner" : {
        "plannerVersion" : 1,
        "namespace" : "engine.message",
        "indexFilterSet" : false,
        "parsedQuery" : {
            "$and" : [ 
                {
                    "field_1" : {
                        "$eq" : "ajian"
                    }
                }, 
                {
                    "field_2" : {
                        "$regex" : ""
                    }
                }, 
                {
                    "field_3" : {
                        "$regex" : ""
                    }
                }, 
                {
                    "field_4" : {
                        "$exists" : true
                    }
                }, 
                {
                    "field_5" : {
                        "$exists" : true
                    }
                }, 
                {
                    "field_6" : {
                        "$exists" : true
                    }
                }
            ]
        },
        "winningPlan" : {
            "stage" : "COLLSCAN",
            "filter" : {
                "$and" : [ 
                    {
                        "field_1" : {
                            "$eq" : "ajian"
                        }
                    }, 
                    {
                        "field_2" : {
                            "$regex" : ""
                        }
                    }, 
                    {
                        "field_3" : {
                            "$regex" : ""
                        }
                    }, 
                    {
                        "field_4" : {
                            "$exists" : true
                        }
                    }, 
                    {
                        "field_5" : {
                            "$exists" : true
                        }
                    }, 
                    {
                        "field_6" : {
                            "$exists" : true
                        }
                    }
                ]
            },
            "direction" : "forward"
        },
        "rejectedPlans" : []
    },
    "executionStats" : {
        "executionSuccess" : true,
        "nReturned" : 1537253,
        "executionTimeMillis" : 2536,
        "totalKeysExamined" : 0,
        "totalDocsExamined" : 1610191,
        "executionStages" : {
            "stage" : "COLLSCAN",
            "filter" : {
                "$and" : [ 
                    {
                        "field_1" : {
                            "$eq" : "ajian"
                        }
                    }, 
                    {
                        "field_2" : {
                            "$regex" : ""
                        }
                    }, 
                    {
                        "field_3" : {
                            "$regex" : ""
                        }
                    }, 
                    {
                        "field_4" : {
                            "$exists" : true
                        }
                    }, 
                    {
                        "field_5" : {
                            "$exists" : true
                        }
                    }, 
                    {
                        "field_6" : {
                            "$exists" : true
                        }
                    }
                ]
            },
            "nReturned" : 1537253,
            "executionTimeMillisEstimate" : 2417,
            "works" : 1610193,
            "advanced" : 1537253,
            "needTime" : 72939,
            "needYield" : 0,
            "saveState" : 12588,
            "restoreState" : 12588,
            "isEOF" : 1,
            "invalidates" : 0,
            "direction" : "forward",
            "docsExamined" : 1610191
        },
        "allPlansExecution" : []
    },
    "serverInfo" : {
        "host" : "secret",
        "port" : 27017,
        "version" : "3.4.10",
        "gitVersion" : "2234234232325323343"
    },
    "ok" : 1.0
}

Why is mongo"s count count so slow? How do the gods solve this problem when they do paging? How should I solve this problem?