I’m not sure what you mean exactly by laggy, but to me running Windows 10 on this Mac Mini ”feels” to me like the difference between running Mac OS X on a power PC machine vs an Intel machine.
The OS itself appears to be ok - not lightening fast but no different from Windows 7. Where it is laggy is in playing video, what you can see is the video pause for a fraction of a second and then jump slightly to catch up. Same video, played by the same software on Windows 7 played perfectly.
After the upgrade I didn't reinstall and drivers, or boot camp assistant although I have not subsequently updated the graphics card driver without any impact. Was there anything you did post upgrade to get your machine working smoothly?