Multishop (same theme and modules) but one shop is slower

[sadlyblue]

Hi,

 

We have been using prestashop in multishop mode for quite some time now.

But always the same theme, and only share categories and products between them.
 

We have found that the loading time is different for each shop. And it seems the more customers it has registered, the more it takes to load.
If shop 1 has 1000 customers, and shop 2 has 200, shop 2 loads faster. I doesn't make sense to us.

 

What could be delaying this?

I check the modules (module_shop table), are exactly the same for all shops. Same discounts in specific_price tables...

Any insights?
 

Thanks