You haven't mentioned your PC's specs; CPU, RAM, storage type, etc. In any case, when running an OS inside a virtual machine using Vbox or any other similar software, performance is mostly limited by hardware, so the stronger the hardware, the better the performance, it's nothing to do with "running an OS inside another OS". For example, If your pc has a dual-core CPU and 8 gigs of RAM, the VM will use 1 core and a max of 4 gigs of RAM, which is not enough by today's standards, so performance will be poor, on the other hand, if the PC has a quad-core CPU (8 threads) and 16 gigs of RAM, the VM can use up to 4 cores and 8 gigs of RAM, so performance will be better, in other words, the more resources the host machine has (CPU cores and RAM), the better the VM will perform. That said, it'll never be as fast and responsive as running in bare metal (installed in the real machine). So your best bet is to follow
@Condobloke suggestion; download, burn/write to a USB, and boot from it the system, you'll get a better/closer feeling to how really well the system performs in your PC.