I had similar experiences with Virtualbox; especially when CPU is Corei3 (corei5, corei7 and better less issues)
Make sure to disable the Virtual Memory in windows if you have enough RAM, or make it fixed - at least 4GB. If you do not share resources, disable the "server" service. make sure you set performance to background services and "Adjust to best performance". Do not use any background pictures and disable power saving features.