Yes, Hyper-V is known to slow down Windows 10. To be able to determine if indeed that Hyper-V slows down the Windows system, you may have to perform synthetic benchmarks before and after enabling Hyper-V. The result will likely show that with Hyper-V enabled, even if you have no VMs running, there is a performance hit. At times, the Hyper-V virtual machine might be slow to start - but you can speed it up!