Hi,
I doubt that the problem is with the number of products. 28000 isn't that much products. I've seen HikaShop websites with 100 times that with product pages loading in less than 1 second.
So your problem is probably with some setting.
But I can't tell without looking at what you have done.
Please provide a link to such page and a backend access so that we can check your settings.
PS: please don't post your questions both in the forum and via the contact form. It's more work for us and thus slower answers for everyone.