SELECT 
  cscart_product_feature_variant_descriptions.variant, 
  cscart_product_feature_variants.variant_id, 
  cscart_product_feature_variants.feature_id, 
  cscart_product_features_values.variant_id as selected, 
  cscart_product_features.feature_type 
FROM 
  cscart_product_feature_variants 
  LEFT JOIN cscart_product_feature_variant_descriptions ON cscart_product_feature_variant_descriptions.variant_id = cscart_product_feature_variants.variant_id 
  AND cscart_product_feature_variant_descriptions.lang_code = 'en' 
  LEFT JOIN cscart_product_features_values ON cscart_product_features_values.variant_id = cscart_product_feature_variants.variant_id 
  AND cscart_product_features_values.lang_code = 'en' 
  AND cscart_product_features_values.product_id = 240 
  AND cscart_product_features_values.feature_id = cscart_product_feature_variants.feature_id 
  LEFT JOIN cscart_product_features ON cscart_product_features.feature_id = cscart_product_feature_variants.feature_id 
WHERE 
  1 
  AND cscart_product_feature_variants.feature_id IN (15, 16) 
GROUP BY 
  cscart_product_feature_variants.variant_id 
ORDER BY 
  cscart_product_feature_variants.position, 
  cscart_product_feature_variant_descriptions.variant

Query time 0.00099

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "cscart_product_feature_variants.position, cscart_product_feature_variant_descriptions.variant",
      "temporary_table": {
        "nested_loop": [
          {
            "table": {
              "table_name": "cscart_product_feature_variants",
              "access_type": "ALL",
              "possible_keys": ["feature_id"],
              "rows": 158,
              "filtered": 24.68354416,
              "attached_condition": "cscart_product_feature_variants.feature_id in (15,16)"
            }
          },
          {
            "table": {
              "table_name": "cscart_product_feature_variant_descriptions",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY"],
              "key": "PRIMARY",
              "key_length": "9",
              "used_key_parts": ["variant_id", "lang_code"],
              "ref": [
                "n764025_kutubminar123.cscart_product_feature_variants.variant_id",
                "const"
              ],
              "rows": 1,
              "filtered": 100,
              "attached_condition": "trigcond(cscart_product_feature_variant_descriptions.lang_code = 'en')"
            }
          },
          {
            "block-nl-join": {
              "table": {
                "table_name": "cscart_product_features_values",
                "access_type": "range",
                "possible_keys": [
                  "PRIMARY",
                  "fl",
                  "variant_id",
                  "lang_code",
                  "product_id",
                  "fpl",
                  "idx_product_feature_variant_id"
                ],
                "key": "idx_product_feature_variant_id",
                "key_length": "3",
                "used_key_parts": ["product_id"],
                "rows": 2,
                "filtered": 96.79299927,
                "attached_condition": "cscart_product_features_values.product_id = 240 and cscart_product_features_values.lang_code = 'en'",
                "using_index": true
              },
              "buffer_type": "flat",
              "buffer_size": "31KiB",
              "join_type": "BNL",
              "attached_condition": "trigcond(1) and trigcond(cscart_product_features_values.variant_id = cscart_product_feature_variants.variant_id and cscart_product_features_values.product_id = 240 and cscart_product_features_values.feature_id = cscart_product_feature_variants.feature_id and cscart_product_features_values.lang_code = 'en')"
            }
          },
          {
            "table": {
              "table_name": "cscart_product_features",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY"],
              "key": "PRIMARY",
              "key_length": "3",
              "used_key_parts": ["feature_id"],
              "ref": [
                "n764025_kutubminar123.cscart_product_feature_variants.feature_id"
              ],
              "rows": 1,
              "filtered": 100
            }
          }
        ]
      }
    }
  }
}