magento2.2.2 – Magento 2.2.2 Running super slow. Like a snail

I'm not a developer, but I'm working with developers who simply can not solve my speed problems.

We have very good hosting, so I know that's not the problem.
Our site is huge and there are still more extensions and things that should be added.

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 sitting around 7 seconds. I need it in less than 3 seconds.

I'm surprised that someone is even buying.

They say they have passed and cleaned all the code.

I read something about changing it from the default mode to help accelerate. But we need constant access to the back-end to update products and products. Change the photos and all that jazz.

Should 2.2.2 be able to work in less than 3 seconds regardless of the size of my site? www.dimples.co.nz

Frustrated and I need help please