Font size alone is not a good indication as to whether a text is easy to read, it is the x-height what really makes a difference to readability, see explanation below.
Instead of providing font sizes for our titles, we encourage our customers to print out a sample page of the title they are interested in to see whether the type of font and the fonts size are acceptable to them. Please note that viewing the page on the screen will not show the real size (unless you have your monitor properly calibrated for that purpose).
Point size vs. x-Height
The point size of a typeface (Font Size) is a measure of its overall height, from the top of the tallest character above the baseline to the longest descender below the baseline.
x-Height refers to the distance between the baseline that letter sits on and the top of the lower case x (the source of the term) and mid-section of lower case letters.