1/2" UNF Aircraft grade aluminium silencer adapter for the P15 MK II - Just remove the stock thread protector, thread this piece on and thereafter, thread your air rifle silencer on. Works like a charm. Besides your P15's barrel shroud doing its job, this adapter will help take that hoarse growl out of your rifle and permit for a more backyard friendly purr, despending on your option of silencer, of course.
However, the chief complaint here being that, an added silencer will add more length to the rifle, defeating the purpose of having a bullpup rifle in the first place.
However, to that end, we have the bullpup rifle bag available that allows you to store your rifle w/ your silencer attached, please see this bullpup bag.