PLEX performance problem

I’ve upgraded to My cloud home from MBL for several months.
Now i mainly use the MCH as a media server.
the included DLNA server works fine.
But when I use the plex app on my iPad or iPhone, It seems the MCH’s performance is limited, it only works fine when streaming 3Mbps video, when I play a HD video up to 10Mbps, the video always pause and the Plex would remind that the PLEX server’s performance is not high enough.

The My Cloud Home has 1 GB of memory and a Realtek 1.4 GHz A53 Quad Core processor. Plex Server may need more memory, CPU to steaming different types of media content. Here are some Plex Resources explaining Plex requirements.

https://support.plex.tv/articles/201774043-what-kind-of-cpu-do-i-need-for-my-server
https://support.plex.tv/articles/201373793-is-plex-media-server-on-a-nas-right-for-me