2nd class blue Machin security from retail booklet, 2015, coded ROYAL MTIL M15L
The M15L version of these booklets appeared in mid-April 2015.
Cylinder numbers are W6 (blue) W1 (iridescent) W3 (phosphor).
SG U2963 - also used for other years
At the beginning of February 2016 booklets were found with the new printed backing paper. These have the 2015 year code O15R. Future printings in 2016 are expected to have the O16R year code. Some booklets are also available.
Price is for a single stamp.