I plan on using a cnc router to cut this and I have a 17 in round pc of wood I am cutting so something around 14 or 15 inches maximum I think would be good
a 15" full body portrait is tricky - this is only 14" to fit in a 17" circle with 1/2" margin
filename ending with = is good for routing inside the lines - filename ending with ~ is good for engraving on the lines
that sure is a very nice grandma picture - let me know how it turns out