SELECT 
  v.variant_id, 
  v.product_id, 
  vd.variant, 
  vf.position, 
  vf.color 
FROM 
  cscart_product_features_values v 
  LEFT JOIN cscart_product_feature_variant_descriptions vd ON v.variant_id = vd.variant_id 
  AND vd.lang_code = 'en' 
  LEFT JOIN cscart_product_feature_variants vf ON v.variant_id = vf.variant_id 
WHERE 
  1 
  AND v.feature_id = 348 
  AND v.product_id IN (
    '31880', '31882', '31881', '31871', 
    '31879', '31878', '31877', '31876', 
    '31875', '31874', '31873', '31872', 
    '31870', '31869', '19187'
  )

Query time 0.00140

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "13.90"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "v",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "feature_id",
            "product_id"
          ],
          "key_length": "6",
          "rows_examined_per_scan": 15,
          "rows_produced_per_join": 15,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "1.90",
            "eval_cost": "1.50",
            "prefix_cost": "3.40",
            "data_read_per_join": "11K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id"
          ],
          "attached_condition": "((`chocoramo`.`v`.`feature_id` = 348) and (`chocoramo`.`v`.`product_id` in ('31880','31882','31881','31871','31879','31878','31877','31876','31875','31874','31873','31872','31870','31869','19187')))"
        }
      },
      {
        "table": {
          "table_name": "vd",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "chocoramo.v.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 15,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "3.75",
            "eval_cost": "1.50",
            "prefix_cost": "8.65",
            "data_read_per_join": "45K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      },
      {
        "table": {
          "table_name": "vf",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id"
          ],
          "key_length": "3",
          "ref": [
            "chocoramo.v.variant_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 15,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "3.75",
            "eval_cost": "1.50",
            "prefix_cost": "13.90",
            "data_read_per_join": "17K"
          },
          "used_columns": [
            "variant_id",
            "color",
            "position"
          ]
        }
      }
    ]
  }
}