Have you taken a test ride?

Seat tube length, though the traditional way to size bikes, is really a poor way to do it, especially with mountain bikes.

As another poster has alluded to, it's the length of the bike that is more important. You just need enough stand over clearance to comfortably straddle the bike (and dismount in an emergency), but it's the length that determines how comfortable you'll be while riding. Personally, I prefer the shortest frame I can get that gives me a good length. Length refers to the distance between the centers of the head and seat tubes measured parallel to the ground; aka the top tube length (or effective top tube length for sloping TTs).

Each model will only have so many effective TTs, so we fine-tune with stem length (NEVER the fore-aft position of the saddle, which is for positioning the saddle relative to the bottom bracket). Typical range of stem lengths is about 80-120mm.

So, take a test ride and see how it feels.

For reference, I'm 5'8" and ride a 16" frame with 545mm effective top tube and 120mm stem. I also had to replace the 350mm stock seat post with a 400mm one because the old post would have had the minimum insertion line be exposed by a few millimeters.