Whats the application? You can just put a length of 15mm between 2 of them and achieve the same, spendy way if going about it though.
Maybe if you explain then job that needs doing can suggest some options?
I have basically bought the wrong fitting for my speedfit pipes intended on feeding the bathroom sink once it is fitted. I had bought a pushfit 15mm - 1/2" female thread. The tails for the taps are also female 1/2" thread. I was hoping the male - male 1/2" threaded connectors were readily available for less than a couple of these: https://www.screwfix.com/p/jg-speedfit-brass-push-fit-adapting-male-cylinder-coupler-15mm-x/23662
I'll end up just buying the above.