Virtuemart 2 search module

[centurius]

Hi,

I am using eshop with almost 200 000 products and it's too slow,
but when I tried to use memcache to speed up, then arose a problem with search module,

it is working for the first searched product, but when I am trying to search a new product before cache time expiration,
there are still results from previous searching displayed

Joomla ver : 2.5.14
Virtuemart ver : 2.0.22b
PHP ver : 5.4.44
MySQL : 5.5.45

if somebody could help me, it would be perfect
Thank you very much

Rado