We did offer the 15mm grid ...
Published by Colin Beattie, CEO at Supawood
We did offer the 15mm grid as a standard option for many years. The standard drawings are as attached and stored in S:\Master Shop Drawings\1100 SW400 SERIES (SUPATILE)\Superceded
The panel size is 1193 x 593 with a rebate size 5mm wide x 7mm deep.
As mentioned below the grid is very easy to bend or kink sideways during installation so was not popular with installers and we didn't have that much call from architects so chose to discontinue it as a standard option.
It is an easy custom option, although there would be value in giving the installer headsup to allow for extra grid and care in handling.