Load Time Very Slow: Help with working out how to fix?

Hi there WPMU Dev,
I am having trouble with the page load speed of my network. Everything is taking so much longer to load now. I imagine it is a plugin/s. It's just I am at the problem where I need the current plugins installed, yet I don't know how to manage it so that they don't affect the page load time (majorly). Originally I thought the issue was with the Multisite Privacy Plugin (see this topic: https://premium.wpmudev.org/forums/topic/page-speed-dramatically-increases-with-multisite-privacy), however since deactivating that the problem has still returned.

I will turn on the remote access to for the Devs, as I hoping one you guys will be able to log in and check out the plugins I have active and tell whats is best to do. I always get frustrated at this point because I am never sure what to do, but I know I can' afford to not use all the plugins.

You're help with this would be great.

Cheers,

Nim