Aw shucks! That's why I prefer using a scope instead of a meter.Pi is not relevant here.
The limit is an instantaneous value of 15V, which is 2V below the average value. Let's take this peak value of 2V. The waveform of ripple is constituted of a broken segment of sinewave and a segment of exponential. In a decent system, the two segments can be assimilated to straight lines, so we can use a triangle waveform for the actual ripple waveform.
The average value of a triangle wave is half its peak value, so the averaging meter should indicate less than 1V for correct operation. A true-rms meter should register about 1.15V.
P.S: I'm not the teacher here.
B.S. You just taught me a lesson!