SELECT 
  f.feature_id, 
  f.purpose, 
  p.product_id, 
  p.parent_product_id, 
  g.id, 
  g.code 
FROM 
  cscart_product_variation_group_features AS f 
  INNER JOIN cscart_product_variation_groups AS g ON f.group_id = g.id 
  INNER JOIN cscart_product_variation_group_products AS p ON f.group_id = p.group_id 
WHERE 
  p.product_id IN (
    16346, 16348, 15749, 16347, 16338, 15753, 
    16340, 15747, 16351, 15750, 15746, 
    16337, 16336, 15745, 15734, 15741
  )

Query time 0.00125

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.06379896,
    "nested_loop": [
      {
        "table": {
          "table_name": "p",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "idx_group_id"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "loops": 1,
          "rows": 16,
          "cost": 0.01790776,
          "filtered": 100,
          "attached_condition": "p.product_id in (16346,16348,15749,16347,16338,15753,16340,15747,16351,15750,15746,16337,16336,15745,15734,15741)"
        }
      },
      {
        "table": {
          "table_name": "f",
          "access_type": "ref",
          "possible_keys": ["idx_group_id"],
          "key": "idx_group_id",
          "key_length": "3",
          "used_key_parts": ["group_id"],
          "ref": ["u508912950_dev_2025.p.group_id"],
          "loops": 16,
          "rows": 1,
          "cost": 0.03076096,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "g",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["id"],
          "ref": ["u508912950_dev_2025.p.group_id"],
          "loops": 16,
          "rows": 1,
          "cost": 0.01513024,
          "filtered": 100
        }
      }
    ]
  }
}