15mm compression fittings use the same thread as 1/2" male fittings, although the ends are internally tapered to seal against the olive. The type of hose connector you show will have a 1/2" female thread in the nut. A washer will be needed to make the seal. Ideally the compression fitting will have a male 1/2" thread which has a flatter end.
A simpler way to achieve the same end is to compress a 15mm olive onto copper pipe, then work the 1/2" hose over the pipe and olive. Once a cm. or so of hose is past the olive, it can be held securely in place with a hose clip. The hose may need warming to stretch over the copper and this will not work if the hose bore is less than 1/2".