SELECT 
  cscart_product_prices.product_id, 
  COALESCE(
    cscart_master_products_storefront_min_price.price, 
    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 
  LEFT JOIN cscart_master_products_storefront_min_price ON cscart_master_products_storefront_min_price.product_id = cscart_product_prices.product_id 
  AND cscart_master_products_storefront_min_price.storefront_id = 1 
WHERE 
  cscart_product_prices.product_id IN (
    8816, 15145, 8808, 7341, 7343, 7342, 
    7344, 10061, 7658, 7873, 7875, 7874, 
    7347, 7833, 7823
  ) 
  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 0.00094

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_master_products_storefront_min_price",
      "access_type": "system",
      "possible_keys": ["PRIMARY"],
      "rows": 0,
      "filtered": 0,
      "const_row_not_found": true
    },
    "table": {
      "table_name": "cscart_product_prices",
      "access_type": "range",
      "possible_keys": ["usergroup", "product_id", "lower_limit", "usergroup_id"],
      "key": "product_id",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 15,
      "filtered": 80,
      "index_condition": "cscart_product_prices.product_id in (8816,15145,8808,7341,7343,7342,7344,10061,7658,7873,7875,7874,7347,7833,7823)",
      "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}

Result

product_id price
7341 3990.00000000
7342 2790.00000000
7343 2790.00000000
7344 2790.00000000
7347 3990.00000000
7658 3990.00000000
7823 3290.00000000
7833 2990.00000000
7873 5990.00000000
7874 6590.00000000
7875 5490.00000000
8808 1990.00000000
8816 590.00000000
10061 3990.00000000
15145 1990.00000000