SELECT 
  pfv.feature_id, 
  pfv.product_id, 
  pfv.variant_id, 
  gp.group_id 
FROM 
  cscart_product_features_values AS pfv 
  INNER JOIN cscart_product_variation_group_products AS gp ON pfv.product_id = gp.product_id 
  INNER JOIN cscart_product_variation_group_features AS gpf ON gpf.group_id = gp.group_id 
  AND gpf.feature_id = pfv.feature_id 
WHERE 
  pfv.lang_code = 'vi' 
  AND gp.group_id IN (
    15782, 15779, 15535, 15537, 15536, 15774, 
    15773, 15522, 15778, 15523, 15525, 
    15532, 15530, 15771, 15776, 15777, 
    15534, 15533
  )

Query time 0.00298

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "gp",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "idx_group_id"],
          "key": "idx_group_id",
          "key_length": "3",
          "used_key_parts": ["group_id"],
          "rows": 52,
          "filtered": 100,
          "index_condition": "gp.group_id in (15782,15779,15535,15537,15536,15774,15773,15522,15778,15523,15525,15532,15530,15771,15776,15777,15534,15533)"
        }
      },
      {
        "table": {
          "table_name": "gpf",
          "access_type": "ref",
          "possible_keys": ["PRIMARY", "idx_group_id"],
          "key": "idx_group_id",
          "key_length": "3",
          "used_key_parts": ["group_id"],
          "ref": ["dev_db.gp.group_id"],
          "rows": 1,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "pfv",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "idx_product_feature_variant_id",
          "key_length": "12",
          "used_key_parts": ["product_id", "feature_id", "lang_code"],
          "ref": ["dev_db.gp.product_id", "dev_db.gpf.feature_id", "const"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "pfv.lang_code = 'vi'",
          "using_index": true
        }
      }
    ]
  }
}