Very slow query execution

-- HikaShop version -- : business 2..4
-- Joomla version -- : 3.3.6
-- PHP version -- : 5.3+ / 5.4

Hello,

I am in the middle of a migration process from J2.5 to J3.
I had my dev version almost completed and wanted to transfer the latest data from the live website.
I updated hika to the latest release on J2.5 and then export - import the tables to the new J3.

But now any Hika category product pages are loading too slow (about 1 minute to load).
There is particularly one query (the one that counts the published items of the current category) that takes up to 1 minute to execute :

SELECT count( DISTINCT b.product_id) 
  FROM zi2e5_hikashop_product_category AS a 
  LEFT JOIN zi2e5_hikashop_product AS b 
  ON a.product_id=b.product_id 
  WHERE b.product_published=1 
  AND b.product_type = 'main' 
  AND a.category_id IN (12) 
  AND (b.product_access = 'all' OR b.product_access LIKE '%,15,%') 
  ORDER BY a.ordering ASC

I guess that this was something related with the tables optimization. The MySQL tool, was unable to display the exact total number of the records. Whatever I did try to re-create the table's index didn't give me the desired results.
Finally I deleted the tables and re-imported them.
Now the query executes fine.