Why is GNOME running heavier than KDE?

I've tried both, Ubuntu GNOME 16.04 and Kubuntu 16.04 on my ThinkPad and I noticed GNOME heats up my device and causing lags while Kubuntu is giving me a pleasant and efficient experience.

I use Nouveau as my display driver on both (because more problems occur when I use Nvidia drivers). EDIT: p.s. Nvidia causes more resource abuse with my Ubuntu GNOME.

I really like the simplicity of GNOME and I'm planning to make Ubuntu GNOME my daily driver, but I'm opposed with its heaviness and resource abuse. Is there anything I can do to overcome these problems?

EDIT: I have shared this question on r/GNOME and got answers. Thanks guys.