Of the two, the HP. More powerful hardware (CPU and GPU) by quite a lot.
The Dell has a 4k screen, but that's arguably somewhat wasted at 15.6". It also doesn't end up all that much lighter due to the glass touchscreen, which adds back a certain amount of weight. I have a different Dell Inspiron that has a similar design, and while I used the touchscreen because it has one, I could happily live without it.
While it's a '2 in 1' it's damn heavy to use as a tablet - and mine's the 13" version, nevermind what a 15.6" would be like.
So, the Dell's spec is a lot weaker, while the things it offers instead are frankly not going to be all that attractive to most people. Therefore, the HP is my firm recommendation between them,