VM RAM issue

I have a general question about test machine setup.

 

I'm running  Windows Server 2016 with 24GB of RAM.

 

I'm trying to run:

TestComplete 12.50 on the Host (WS2016)

2 VM's running TestExecute (Windows 10) with 4GB of RAM each. 

 

I use VirtualBox for the VM's. For some reason, I can't allocate enough memory for the second VM.

 

I attached my memory specs with 1 VM running. It says I have 7GB available, yet VB can't allocate 4GB?

 

I also posed this question on Oracles site, but have any of you ran into this issue yourselves?