GeForce GTX 1080 Ti (456.71 driver, cause the last NVIDIA driver make crashes with Premiere...).
The test I did is simple: new project (in the same drive path), the first one with Premiere 2019 (13.5) and the second one with Premiere 2020 (14.8). Importing a mp4 clip in a 1080 sequence, playback with no render. Result? Premiere 2019 works fine, Premiere 2020 plays with awful lags. So where is the problem? What's the fix suggestet from Adobe?