I tried to run it in Chrome, (with no other tabs open) on a laptop with the following specs :
- processor: Intel i7-6700HQ
- ram: 16GB
- graphics: Nvidia GTX960M
- system: Windows 10, x64
Personally I have not had much success in getting a good performance out of Unity's HTML output, except for extremely simple prototypes. However there may be tricks to it that I am not aware of.
Good luck! :)