I was debating this, and I ended up just reusing my 14700 (non-K) system as an Unraid box instead of buying a new "15th gen" Intel system. 14th gen still has hyperthreading also on the P-cores. Plus, I got to build myself a new computer for daily use .
I don't see any big disadvantages of the 14th gen systems as long as you have the bios mitigations done so your CPU doesn't burn out.