Virtuemart XHR wait times

[patben]

Hi
I have a "problem" with the  requests of virtuemart like this

index.php? option = com_virtuemart & nosef = 1 & view = productdetails & task = recalculate & virtuemart_product_id = & format = json & customPrice

The wait times are too big like 1.20 seconds and that affect whole page load time.
What could be wrong and what can I do to improve this


Thank you very much