Looks right to me.
I have this chart printed out and taped on the wall behind every sewing machine I use:
https://tolindsewmach.com/thread-chart.html
Also, it says 31-15 on the front. I'd operate on that assumption.
I'd use a small pull type postal scale and set that bottom tension to 1 ounce.
It works great on domestics and, really, you're in that range in terms of thread size, bobbin and needles. If nothing else, it's a known, consistent starting point.