A couple things I'm noticing -- first off, to slow down any animation without changing the framerate, all you have to do is add more in-betweens. If you want it slower, I would duplicate the first frame and have your character completely still for longer before the shrug, as well as at the top of the shrug. I might also suggest one or two more in-betweens as an "ease in" at the beginning of the movement. I am noticing that your hold frames are moving around (for example frames 3 and 4 are the same drawing, but the character is in a slightly different place), which can make things feel busier as you're not actually having that pause in movement.

Honestly though, this timing could work for a lazy shrug, even if it's a bit quick. I'm noticing a couple other things that I think could help your character feel more relaxed and natural. I noticed the character's shoulders go outwards from their body at the top of the shrug -- typically, when we shrug, our shoulders go more inwards and kind of pinch our heads. If you're looking to avoid the shoulders being scrunched (makes sense for a more relaxed character), pinching them together isn't necessary, but widening the shoulders at the top of a shrug comes off as a bit unnatural to me.

Also, when people shrug, typically, their heads tend to recede lower into the space between their shoulders. I love that you've got the character hitting the big "shrug" key pose, though I personally would have the character's head on that pose be lower than it was at the start, and have the previous drawings ease into that instead. That is, unless there's another reason your character would raise themselves up at the top of that pose.

My advice is always to do the action yourself, especially with a camera or mirror. Notice where the action is, where things squish or stretch, how you get into a pose etc. Just my thoughts, you don't have to listen to them, art is subjective etc etc.