SELECT 
  DISTINCT product_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    10256, 10257, 10274, 10275, 10282, 10285, 
    10293, 10294, 10295, 10297, 10301, 
    10303, 10306, 10307, 10309, 10315
  ) 
  AND feature_id IN (116) 
  AND (
    UPPER(value) IN ('Y', 'YES', 'TRUE', '1') 
    OR value IN (
      '해외구매대행', '수입품', 
      'Imported'
    ) 
    OR value_int > 0
  )

Query time 0.00048

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_features_values",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "fl",
        "product_id",
        "fpl",
        "idx_product_feature_variant_id"
      ],
      "key": "fpl",
      "key_length": "6",
      "used_key_parts": ["feature_id", "product_id"],
      "rows": 16,
      "filtered": 100,
      "index_condition": "cscart_product_features_values.feature_id = 116 and cscart_product_features_values.product_id in (10256,10257,10274,10275,10282,10285,10293,10294,10295,10297,10301,10303,10306,10307,10309,10315)",
      "attached_condition": "ucase(cscart_product_features_values.`value`) in ('Y','YES','TRUE','1') or cscart_product_features_values.`value` in ('해외구매대행','수입품','Imported') or cscart_product_features_values.value_int > 0"
    }
  }
}