Question about Synology DS224+

This memory is accepted by NAS but only 6 GB can be used. So there is no point in ordering this.

Well, interesting question.
Actually, the answer should clearly be no, as Synology says here https://www.synology.com/en-us...
says that the maximum memory is limited to 6 GB.
On the other hand, PHS advertises the bar precisely for this NAS.
Since the latter is the case, I would personally leave it at that and try it out. If the 16 GB are not recognised, then just send it back