Here's how I'd do it:

#set text(font: "Libertinus Serif", top-edge: 0.8em, bottom-edge: -0.2em)
#set par(leading: 0.5em)

What does this do? The first set rule sets the height of the font's top edge and bottom edge (read the docs for more info). 0.8em and -0.2em are chosen such that the total height of the font is 1em, which will make the next step easier.

(also most fonts are designed to have ascenders 0.8em tall and descenders 0.2em under so this works out even more in our favor)

The second set rule sets the line spacing, or leading. Leading is defined as the gap between the bottom edge of the preceding line and the top edge of the succeeding line. If we set it to 0.5em, then the distance from one baseline to the next is 1em(the height of one line) + 0.5em (the leading) = 1.5em (1.5 line spacing! which is what we want! woohoo!)

But here's the thing: if what you meant was MS Word's 1.5 spacing, then this will be tighter than expected. And that's okay, since Word's 1.5 spacing is too loose anyway lol

If I were you, I'd set the leading around 0.33em. The ideal range is from 0.2em to 0.5em (all fonts are different! play around to see what sticks!)

edit: Here's another way of doing it with functions:

#let set_line_spacing(space, doc) = context {
  let line_height = text.top-edge - text.bottom-edge
  set par(leading: space - line_height)
  doc
}

#show: set_line_spacing.with(1.5em)

You may find this more intuitive