On general case of accessibility:
I like the idea of keeping the base-font for paragraphs to the default 16px which all browsers have set as default font-size.
This would increase the text-size by 6-7% (16px/15px = 1,0666).
For mobile devices like Phones and Tablets this looks okay. For desktop this would be slightly to big and unusual.
If we go this way, maybe implement some special rule for non-touch-devices to use 15px base-font instead. (By checking for non-touch-devices we definitely miss some notebooks with touch-screens - they then get the bigger font-size.)