SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    12102, 12103, 12104, 12105, 12106, 12107, 
    12108, 12109, 12110, 12111, 12112, 
    12113, 12114, 12115
  ) 
  AND feature_id IN (553, 622) 
  AND lang_code = 'en'

Query time 0.00327

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "12.45"
    },
    "table": {
      "table_name": "cscart_product_features_values",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "fl",
        "lang_code",
        "product_id",
        "fpl",
        "idx_product_feature_variant_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "feature_id",
        "product_id"
      ],
      "key_length": "6",
      "rows_examined_per_scan": 53,
      "rows_produced_per_join": 22,
      "filtered": "42.69",
      "using_index": true,
      "cost_info": {
        "read_cost": "10.19",
        "eval_cost": "2.26",
        "prefix_cost": "12.45",
        "data_read_per_join": "17K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`gaseus`.`cscart_product_features_values`.`product_id` in (12102,12103,12104,12105,12106,12107,12108,12109,12110,12111,12112,12113,12114,12115)) and (`gaseus`.`cscart_product_features_values`.`feature_id` in (553,622)) and (`gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}