SELECT 
  cscart_product_prices.product_id, 
  MIN(
    IF(
      cscart_product_prices.percentage_discount = 0, 
      cscart_product_prices.price, 
      cscart_product_prices.price - (
        cscart_product_prices.price * cscart_product_prices.percentage_discount
      )/ 100
    )
  ) AS price 
FROM 
  cscart_product_prices 
WHERE 
  cscart_product_prices.product_id IN (
    2307, 2306, 2308, 13820, 11805, 2335, 
    2216, 2217, 15142, 2220, 2803, 2264, 
    2262, 13109, 13110, 12701, 2580, 4394, 
    2769, 2768, 2767, 2766, 12700, 13840, 
    2224, 15149, 2192, 2191, 15146, 15147
  ) 
  AND cscart_product_prices.lower_limit = 1 
  AND cscart_product_prices.usergroup_id IN (0, 1) 
GROUP BY 
  cscart_product_prices.product_id

Query time 0.00790

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "cscart_product_prices.product_id",
      "temporary_table": {
        "table": {
          "table_name": "cscart_product_prices",
          "access_type": "ref",
          "possible_keys": [
            "usergroup",
            "product_id",
            "lower_limit",
            "usergroup_id"
          ],
          "key": "lower_limit",
          "key_length": "3",
          "used_key_parts": ["lower_limit"],
          "ref": ["const"],
          "rows": 6449,
          "filtered": 6.735769272,
          "attached_condition": "cscart_product_prices.lower_limit <=> 1 and cscart_product_prices.product_id in (2307,2306,2308,13820,11805,2335,2216,2217,15142,2220,2803,2264,2262,13109,13110,12701,2580,4394,2769,2768,2767,2766,12700,13840,2224,15149,2192,2191,15146,15147) and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    }
  }
}