Shortcut, shortcut, shortcut. And then do the job again because you didn't do it right in the first place. This is basically the definition of half-assing anything if I've ever seen it. Might work for you, but don't recommend this to others that won't have your same luck.^ And I have direct burial coax that's held up fine. There is no reason to expect ethernet to do worse if you have equal quality cable (sheathing).
This whole topic could have literally been, find it on amazon, it gets delivered a day or two later, the same day you rent the cable trencher and spend an hour installing it.
Even if direct burial cable fails eventually, you could lay it 5 times with less manual labor and time spent, but far before that happens, you'd have moved on, to another residence or to a newer network standard.
Do not think you are going to pull a new ethernet (or fiber optic) cable through 150' of conduit to replace the old, unless you use larger conduit which then raises and cost and labor again, even that factor being more burden than stringing a bare burial cable again.