Reduce the weight of my figma displays without reducing visual quality

I'm currently creating my portfolio, in presentation slide format. Unfortunately, the presentation slides for my web UI screens are heavy, due to the size of the mocked-up screens, so when I export as a pdf, it's extremely heavy! 
I've tried converting the screens to png or images, but the visual quality is terrible. I've tried flattening all the screens, but it breaks all my designs... 
I can't find any solution to reduce the weight of my portfolio without altering the visual quality... do you have any advice?

I hope I have succeeded in being clear in my explanations…

thank you in advance for your advice!