So heres the main issue ok, Your cpu baseclock is 2.0ghz which older celerons werent know as being a very powerful processor by no means, Lets put this in perspective of how powerful it is, A rpi 3 has a more powerful cpu then this celeron. The TDP of this processor is only 10watts of power.
To me this is going to be a normal issue that your gonna have to get used to with a weak processor. Something that may help a bit If you installed ubuntu on the same drive as the node its going to slow everything down. Installing the OS on a different drive would increase performance a bit because its not going to be sharing the same resources as your node is. Another thing is if your running the OS with a GUI its gonna put alot more overhead vs running without a GUI.
My Node is on a pretty weak cpu as well but I have the OS installed on its own SSD, I am running No GUI, It struggles when start up on one node and if its a fresh reboot I have seen it pegged at 100% cpu for a few hours.