Lowest gear ratio available in a folding bike

I'm a wimp & am technically declined so sorry in advance b/c I get confused so may use the wrong jargon.

My train line may take very few whole size bikes in future so I am investigating foldies.
What to do may come down to gear ratios.
My 3 mile commute (thru Norwich) I currently do on bikes that (not counting panniers) have weight/gear ratios =

12 kg, 2.19m
15kg, 2.09m

Those have me at my physical limits to get up hills. I struggle bad with higher GRs.
It seems like with a 6 speed Brompton, 12% reduction, I could get
11-12 kg, 2.32 m gear ratio.

Is 12 kg/2.32m GR the lowest weight/GRatio I could get in an off-the-shelf folder that is also quick /easy to fold & use on the train plus also has mudguards? Seems like every folder will have much higher GR than I want. I doubt 2.32m is low enough. How easy would it be to swap in smaller chain ring on most foldies, Like could I get a Dahon or Birdy & just stick a smaller chain ring on it, easily enough, should default gear ratios be my deciding factor?

Thanks in advance.

I looked at a previous similar thread on Bikeradar, but didn't talk real GR numbers, so maybe not so relevant.
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