Reply To: Font Size for Groups/Comments
You can adjust the font size via filters.
If you don’t know how to use apply_filters, then editing or over-riding the css is another approach.
Look for ‘mini’ and ‘acomment’.
For example, ‘mini’ can be found in
bp-themes\bp-default\_inc\css\responsive.css
bp-themes\bp-default\_inc\css\default.css
bp-themes\bp-default\_inc\css\default-rtl.css