Having 2G for nursery is not that concerning when using 10G max size for heap.
You can probably boost it up to 3G but without examining the verbose gc its just shooting in the dark.

How it works is . in your case 10GB is allocated for heap and 4GB is allocated for the Native Memory usage for the JAVA heap , (this is due to the options used  -Xcompressedrefs ) + some GB for Direct Bytes Buffers.
So potentially you are using all your Physical memory and leaving nothing for OS and other processes.  
In this case maybe you are better off using less heap size.  (8GB )
 
If it turns out to be the problem with Native memory and not the JAVA heap it self then as you can see treatment is different.

Try to see how the heap performance is using JAVA option -verbose:gc

set JAVA_OPTS=%JAVA_OPTS% -verbose:gc
set JAVA_OPTS=%JAVA_OPTS% -Xverbosegclog

Restart the server.

This will start generating the gc log  verbosegc.xxx.xxx.xxx.log which you can check after server started showing a hang. Atleast you would know if the heap is the problem or Native memory is causing too many explicit GC calls. Also check the memory usage of the machine to see if system is paging.

Also look in the log of CCM , JTS , etc which are under same liberty profile to check what errors are getting reported.
They probably will give you some clue what is causing the periodic slow down. This would require a bit of searching on what those errors mean.

Try to pin point the location of the problem.

If above does not help i think its better to open a PMR with IBM support.