Firstly I gather Hyperion does use a small Oracle database but most of the processing is its own engine. Therefore this probably isn't a traditional sort of Oracle system.
So you have a PC with core i5 quad core, 16GB RAM and Windows 7? So my initial guess at single VM sizing would be 3 vCPU and 12GB.
Then you should try using Windows Resource Monitor during your VM startup too to see what seems to be used most - processor, memory or disk. There is a good chance that the disk is the bottleneck at startup. As I think you have a desktop PC it should be easy to add an SSD alongside the boot disk without too much disruption. E.g. even 128GB SSD might perhaps be big enough and should be cheap enough to take a gamble on - just put all your VM files (the folder with the .vmx, .vmdk etc) onto it and leave everything else where it is.
Yes, hyper-threading should make a difference but only if processing is really the biggest constraint. I suspect an SSD will give you the biggest improvement for your money but before you open your wallet it would be worth trying the things above.
Simon
PS. I think I'd tell my nephew to run his games elsewhere when I was trying to work 