magento2.2.2 – Magento 2.2.2 Run very slowly. Like a snail

I am not a developer, but I work with developers who can not solve my speed problems.

We have a very good accommodation so I know this is not the question.
Our site is huge and there are even more extensions and things to add.

I constantly tell developers that the speed is not good enough. This morning, it took 20 seconds to load a product. Last week, he was seated for about 7 seconds. I need less than 3 seconds.

I'm surprised anyone is even shopping on it.

They say that they have gone through and cleaned up all the code.

Have you read anything about changing the default mode to speed up the process? But we need constant back-end access to update products and products. change the photos and all that jazz.

2.2.2 should it be able to work in less than 3 seconds regardless of the size of my site?

Frustrated and need help please