The Rudraaksha Jaabaalopanishad describes the lord and merits of wearing 1 faced to 14 faced Rudraakshas. The Shiva Puraan (Vidyeswara Samhitaa) goes no further.
The Shrimad Devi Bhaagvatam mentions the creation of 38 types of Rudraaksha (10+12+16) but it is not specifically stated that these are differentiated on the basis of faces. The suggested differences are more about the colour of the bead. At any rate it does not describe Rudraakshas with more faces than 14.
I have never read the Kaatyaayani Tantra (as no translation or even printed Sanskrit version seems to be available) but this product page seems to suggest that some details may be available there.
Is there any description of the properties of Rudraakshas with 15 or more faces in any scriptures?