Plex Media Scanner - How do I Limit Memory

I have PMS running on a low spec VPS running ubuntu 16.04 and mounting my Amazon Cloud Drive to the server using acd_cli.

This works ok for me for playing videos. But when I bulk add new content, the Scanner uses all the available memory until it runs out, and then the linux out of memory killer kicks in and kills the acd_cli process which in turn unmounts the cloud drive.

I know the best solution would be to increase the resources of the VPS, but I can't really justify increasing the resources of the VPS, especially as it only seems to be an issue when add new media and scanning, not playback.

So the questions are:

How do I set a limit on the memory used by the scanner ?

I am guessing it would be to use ulimit. I am just not sure where I would set this to apply it to the Plex Media Scanner.

Also, would I be better off using ubuntu 14.04 (Does it use less memory than 16.04) ?

Thanks