I looked for ways to lighten my Brompton. Anyone using marathon/mararthon plus tyres could lose a lot of weight by switching to Primo Comets with a tyre liner.
I switched the SA gear cable outer for a standard gear cable outer and that saved 30g. Perhaps on a six speed both cables are of the SA variety?
The new type of folding pedal nut and washer should save around 20g.
I installed (with some trouble) a cartridge bearing headset which is 60g lighter than the steel type and lighter than the Brompton alloy type.
Some bolts can be switched out for ti equivalents.
When I built a rear wheel I opted for 14g spokes which saves quite a bit of weight.

So there's a few things that can be done which in combination are significant.