Upfront sites are slow to respond

I've asked my customers and developers to use upfront. But it seems that Upfront sites are much much slower than our bootstrap themes. Can we make Upfront snappier? It's such a shame that Upfront is a great wysiwyg editor but suffers from slow loading.

FAQs:

1. We're on AWS
2. Yes we use Nginx and Varnish
3. We have optimised Varnish to work well with wpmudev plugins especially marketpress.
4. We use a lot of wpmudev plugins. If I should turn off any of them, do let me know.