Plastic chain ring protectors are available.
I have upgraded a number of small wheeled folders to rival road race bikes. If you look at some of my threads. Even 16 inch folders can really shift set up correctly.
Agree with comment that tyre is the best speed upgrade. Most cheap folders benfiet from jojack slick high pressures fitting. I then change the bars to lower profile bars and most sit up and beg folders have been transformed.
Folding bikes can go fast with small upgrades in my experience. By the way I used to bike to the station from home and many days me, on a mezzo, and a Moulton rider were speeding pass pretty much all the cyclists and keeping up with the cars. No further prof in my mind required that small wheels can motor.