Improve Google PageSpeed Insights for WordPress Websites

How is it possible to improve UpFront/Spirit? Speed equals profit. I want to use UpFront themes and am determined to improve website loading times. There are two sites I use to find what needs improvement:
https://developers.google.com/speed/pagespeed/insights/?url=https%3A%2F%2Fpremium.wpmudev.org%2F
and
http://tools.pingdom.com/fpt/#!/b3jdB/https://premium.wpmudev.org/
As you can see, wpmudev.org does not score well. By comparison, my sites are MUCH faster:
https://developers.google.com/speed/pagespeed/insights/?url=https%3A%2F%2Ftapness.com%2F
and
http://tools.pingdom.com/fpt/#!/egvkuf/https://tapness.com/
I want to built a multisite with UpFront. The architecture there seems fundamentally different. Is it possible to make a child theme? Is it possible to move the css and js files? Page speed is crucial and going to become increasingly more important. According to Google, phone traffic exceeds laptops. Phones need files much faster through a very limited data channel for very impatient people. Mobile-first design is necessary. Slower means lost revenue. WalMart abandoned their $1million website because it was too slow and started over from scratch built for speed.