I thought it was quite simple to increase the VM-memory beyond the 1500MB limit of the GUI.
However, starting the SOABPM server in the OTN SOABPM appliance would certainly crash the VM. Very nice is the state VirtualBox will bring the VM in: the "Guru Mediation"-Mode.
Well, I would not call myself a VirtualBox-guru, so I wouldn't mediate in why the VM didn't feel as comfortable as it should.  So turn-off the machine.

It turns out that the the 1500MB limit is not as arbitrary as thought. In the Issue Ticket here I read that the VMM process places the complete VM's memory  in the process-memory space. In 32-bit Windows the maximum of the process-address space is 2GB.And 2GB for the kernel. Since there is addresspace needed for the VMM process, the video memory etc., the limit for the VM is set to 1500MB.
I would think that the limit is some further on the "save side", possibly something like 1750MB would do either.

Since I'm a pretty stubborn guy, I'll try 2000MB.  Also to see the "Guru Mediation" mode state again... Then I'll try some saver values.