Hundreds Customfields, shop slowed down

[Adwans]

Hello everybody,
Joomla! 3.4.8
VM 3.0.12
PHP 5.6
http://www.biurodom.hekko24.pl/index.php/vinduer/pvc-vinduer/sidehengslet-vindu/single-window-tilt-turn-white-detail
http://www.biurodom.hekko24.pl/index.php/vinduer/pvc-vinduer/sidehengslet-vindu
I have a webshop with windows, so: due to fact that a single window appears in many sizes - one product has - let say - about 640 sizes. This means 640 custom fields.
From this moment "category view" as well as "product view" slowed down. server response: about 14-15 sec.
Of course: GZIP is on, Joomla cache in conservative mode is on.
Any idea? And why, for the God's sake, category page slowed down too? Does it load products CFs as well in order to display "category view"? (This category HAS 1 product! LINK above)
What should I do - I cant even imagine having more products, for example 150 windows in hundreds sizes!
Should I "dump" pages / change them into static pages/ use any plugin?
I disabled everything in Joomla except VM, backup plugin, some security stuff...K2 blog... in fact I dont need K2, only VM is mandatory.
Regards! Zbyszek

[GJC Web Design]

taking the cat page it definitely seems server related - 17+ sec to respond to the 1st GET with all caches cleared

a subsequent reload only takes 250Ms so it is cached

but what I assume is a plain Joomla page (turn off sef so u can actually see what your loading) is not impressive anyway
http://www.biurodom.hekko24.pl/index.php/home

4.5 sec

What are the server specs?

[VMTemplates.net]

it looks like a server load issue - check server load using WHM
or contact your server/hosting account provider

Thanks,
J.

[jenkinhill]

And after fixing the host consider updating your versions and switching to PHP7 for greater speed.   http://forum.virtuemart.net/index.php?topic=118683.0

[Adwans]

@GJC, @jenkhill, @VMTemplates.net,  thank you for all notices / tests and advises. After upgrading Joomla, VM and switching to PHP7 this bus drives faster ... not Mustang, yet, but - the difference is noticeable.
Maybe hosting parameters is the biggest issue. I will test it. 

[GJC Web Design]

yes-- the suitability of hosts for a Joomla/VM install can vary hugely.. some are just hopeless

[VMTemplates.net]

Try VPS or dedicated. Prices are higher than cheap shared hosting accounts but its worth to spend a little more to improve performance (also for further seo works).