As @arslankayna suggests, add the following to your sys.txt:

[interface]
mapfontscale3dframed=203

then play with different values, for your resolution I would start at around 100 rather than 203

Note: this will change the size of framed street names and other names like suburbs, streams etc., but ONLY when you have

[3d_config]
roadsign_always_framed=1

in your sys.txt

I hope this is clear for you