spray that part in red or a gas colour reference then you know what its for
to make that part even better and for other uses
use a soldered 15mm tee and a bit of pipe fit on one end a reducer 15mm too 22mm and a 22mm straight connector the other part is for 15mm push fit cap
create a box air tight pipe testing kit
or
use a push fit 15mm tee
15mm to 22mm reducer a bit of pipe both sides
15mm to 22mm reducer with compression straight on it
22mm straight push fit
15mm push fit cap end
it will give you a full test kit within a box
you can also add your meter test pipe as well sprayed for a reason so you know the difference between them
dont try and think i dont need 2 reducers as you do puch fits wont fit onto conpression ring fitted fittings so best to have 2 versions of a reducer
the compression side of it can be used to screw onto the nut or used to tighten onto a nut on the pipes