I assume you're referring to this speedup mentioned in the release notes?
The performance of several filters, including the Triangle, Sinc, Blackman-Harris, Catmull-Rom, and Mitnet filters have been improved when rendering in progressive mode. In some cases, we have seen a 48% improvement in performance and a 20x improvement in memory usage (ARNOLD-10651).
As mentioned there, you need to be using one of those filters with progressive mode enabled. If you were not (and your scene isn't) then this doesn't apply.
As for the intel denoiser, I just tried enabling it and and didn't see any noticeable slowdown in your scene. Are you sure you're using the intel imager denoiser and not a different denoiser? Or maybe some other settings were changed? If you can collect some info level logs, we can see what's really going on since that will tell us what settings are being used and where the time is going.
Finally, adaptive sampling can help but only if you set the settings properly and the scene has regions with different amounts of noise (so it can adapt the sampling rate to the different regions). If you enable adaptive sampling without lowering the AA and adjusting the threshold, then it's expected that it will make it slower. Lower AA to 3 and raise the threshold until you get the time/quality tradeoff you desire.
