Pipe might be in at a obtuse angle, so no matter how much you tighten it the olive it will not sit in the shamphered brass female part. try doing what the guy said before me with the ptfe tape(have hold of the threaded fitting in left hand,and have ptfe in right hand make sure the tape goes on...
I would put plastic pipe in and only plastic pipe no fittings in wall.
From under floorboards bring pipe up into wall bend slightly at the top clip it up at 45 degree angle.
Put plastic pipe 22 mm over 15 mm pipe..e