I HIGHLY recommend you grab a couple of these: AOC USB Screens [0]. They are cheap, LIGHT, and great. I have two of them with my also 15" Omen laptop.[1] So I have a full size gaming/workstation machine, and TWO external screens, at 1920 while the machine is 2500 resolution... and ALL of this fits in my backpack. and is super light.
(Also, I am designing a bracket using the VESA mount screws on the back of the screens to attach them to the small camera tripods I have which are also very light and fit in backpack - this way, I can mount one screen behind the laptop, and have that screen directly above my laptop screen, and then another to the side.)
[0] https://www.amazon.com/AOC-I1659FWUX-USB-Powered-Portable-19...
[1] https://i.imgur.com/MJNWvif.jpg
(Also, I am designing a bracket using the VESA mount screws on the back of the screens to attach them to the small camera tripods I have which are also very light and fit in backpack - this way, I can mount one screen behind the laptop, and have that screen directly above my laptop screen, and then another to the side.)