Mongo aggregation performance - mongodb

Question

I am new to mongo and below query performs really slow with record set over 2 Million records
Query
db.testCollection.aggregate({
$match: {
active: {
$ne: false
}
}
}, {
$group: {
_id: {
productName: "$productName",
model: "$model",
version: "$version",
uid: "$uid"
},
total: {
$sum: 1
}
}
}, {
$project: {
total: 1,
model: "$_id.model",
version: "$_id.version",
uid: "$_id.uid",
productName: "$_id.productName"
}
}, {
$sort: {
model: 1
}
})
explain()
{
"stages" : [
{
"$cursor" : {
"query" : {
"active" : {
"$ne" : false
}
},
"fields" : {
"version" : 1,
"productName" : 1,
"model" : 1,
"uid" : 1,
"_id" : 0
},
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "fms2.device",
"indexFilterSet" : false,
"parsedQuery" : {
"$nor" : [
{
"active" : {
"$eq" : false
}
}
]
},
"winningPlan" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"active" : 1
},
"indexName" : "active",
"isMultiKey" : false,
"multiKeyPaths" : {
"active" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"active" : [
"[MinKey, false)",
"(false, MaxKey]"
]
}
}
},
"rejectedPlans" : [ ]
}
}
},
{
"$group" : {
"_id" : {
"productName" : "$productName",
"model" : "$model",
"version" : "$version",
"uid" : "$uid"
},
"total" : {
"$sum" : {
"$const" : 1
}
}
}
},
{
"$project" : {
"_id" : true,
"total" : true,
"model" : "$_id.model",
"version" : "$_id.version",
"uid" : "$_id.uid",
"productName" : "$_id.productName"
}
},
{
"$sort" : {
"sortKey" : {
"model" : 1
}
}
}
],
"ok" : 1
}
Is there a way to optimize this query more ? I had a look into https://docs.mongodb.com/manual/core/aggregation-pipeline-optimization/ as well but most of the stated suggestions are not applicable for this query.
Not sure if it matters, result of this aggregation ends up with only 20-30 records.