Optimisation requête SQL Prestashop

La requête suivante du module Blocklayered sur prestashop 1.5.6 prend plus de 10s sur mon serveur dédié. J'aimerais descendre en-dessous de 1seconde.

/modules/blocklayered/blocklayered.php
(autour de la ligne 2010)
SELECT
p.*,
'.($alias_where == 'p' ? '' : 'product_shop.*,' ).'
'.$alias_where.'.id_category_default,
pl.*,
MAX(image_shop.`id_image`) id_image,
il.legend,
m.name manufacturer_name,
MAX(product_attribute_shop.id_product_attribute) id_product_attribute,
DATEDIFF('.$alias_where.'.`date_add`, DATE_SUB(NOW(), INTERVAL '.(int)$nb_day_new_product.' DAY)) > 0 AS new,
stock.out_of_stock, IFNULL(stock.quantity, 0) as quantity
FROM `'._DB_PREFIX_.'category_product` cp
LEFT JOIN '._DB_PREFIX_.'category c ON (c.id_category = cp.id_category)
LEFT JOIN `'._DB_PREFIX_.'product` p ON p.`id_product` = cp.`id_product`
'.Shop::addSqlAssociation('product', 'p').'
'.Product::sqlStock('p', null, false, Context::getContext()->shop).'
LEFT JOIN '._DB_PREFIX_.'product_lang pl ON (pl.id_product = p.id_product'.Shop::addSqlRestrictionOnLang('pl').' AND pl.id_lang = '.(int)$cookie->id_lang.')
LEFT JOIN `'._DB_PREFIX_.'image` i ON (i.`id_product` = p.`id_product`)'.
Shop::addSqlAssociation('image', 'i', false, 'image_shop.cover=1').'
LEFT JOIN `'._DB_PREFIX_.'image_lang` il ON (image_shop.`id_image` = il.`id_image` AND il.`id_lang` = '.(int)$cookie->id_lang.')
LEFT JOIN '._DB_PREFIX_.'manufacturer m ON (m.id_manufacturer = p.id_manufacturer)
LEFT JOIN '._DB_PREFIX_.'product_attribute pa ON (p.id_product = pa.id_product)'.
Shop::addSqlAssociation('product_attribute', 'pa', false, 'product_attribute_shop.`default_on` = 1').'
WHERE '.$alias_where.'.`active` = 1 AND '.$alias_where.'.`visibility` IN ("both", "catalog")
AND p.id_product IN ('.implode(',', $product_id_list).')
AND '.(Configuration::get('PS_LAYERED_FULL_TREE') ? 'c.nleft >= '.(int)$parent->nleft.' AND c.nright &lower;<= '.(int)$parent->nright : 'c.id_category = '.(int)$id_parent).'
AND c.active = 1
GROUP BY product_shop.id_product
ORDER BY '.Tools::getProductsOrder('by', Tools::getValue('orderby'), true).' '.Tools::getProductsOrder('way', Tools::getValue('orderway')).
' LIMIT '.(((int)$this->page - 1) * $n.','.$n));
########################################################
Ce code donne par exemple la requête suivante sur ma base de prod:
########################################################
# Query_time: [Téléphone visible pour les membres Pro] Lock_time: [Téléphone visible pour les membres Pro] Rows_sent: 12 Rows_examined: [Téléphone visible pour les membres Pro]
SELECT
p.*,
product_shop.*,
product_shop.id_category_default,
pl.*,
MAX(image_shop.`id_image`) id_image,
il.legend,
m.name manufacturer_name,
MAX(product_attribute_shop.id_product_attribute) id_product_attribute,
DATEDIFF(product_shop.`date_add`, DATE_SUB(NOW(), INTERVAL 0 DAY)) > 0 AS new,
stock.out_of_stock, IFNULL(stock.quantity, 0) as quantity
FROM `ps_category_product` cp
LEFT JOIN ps_category c ON (c.id_category = cp.id_category)
LEFT JOIN `ps_product` p ON p.`id_product` = cp.`id_product`
INNER JOIN ps_product_shop product_shop
ON (product_shop.id_product = p.id_product AND product_shop.id_shop = 1)
LEFT
JOIN ps_stock_available stock
ON (stock.id_product = p.id_product AND stock.id_shop = 1 )
LEFT JOIN ps_product_lang pl ON (pl.id_product = p.id_product AND pl.id_shop = 1 AND pl.id_lang = 3)
LEFT JOIN `ps_image` i ON (i.`id_product` = p.`id_product`) LEFT JOIN ps_image_shop image_shop
ON (image_shop.id_image = i.id_image AND image_shop.id_shop = 1 AND image_shop.cover=1)
LEFT JOIN `ps_image_lang` il ON (image_shop.`id_image` = il.`id_image` AND il.`id_lang` = 3)
LEFT JOIN ps_manufacturer m ON (m.id_manufacturer = p.id_manufacturer)
LEFT JOIN ps_product_attribute pa ON (p.id_product = pa.id_product) LEFT JOIN ps_product_attribute_shop product_attribute_shop
ON (product_attribute_shop.id_product_attribute = pa.id_product_attribute AND product_attribute_shop.id_shop = 1 AND product_attribute_shop.`default_on` = 1)
WHERE product_shop.`active` = 1 AND product_shop.`visibility` IN ("both", "catalog")
AND p.id_product IN (10,11,12,13,14,15,17,18,20,21,24,25,26,27,28,29,30,31,33,34,35,36,37,38,39,40,45,46,47,48,50,51,52,53,54,55,57,59,61,62,63,65,66,67,68,70,74,76,77,79,81,89,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114)
AND c.nleft >= 3 AND c.nright <= 52
AND c.active = 1
GROUP BY product_shop.id_product
ORDER BY cp.position asc LIMIT 0,12;