A 1.5mm is a size 7 steel crochet hook

Gauge is not critical in this pattern. You can try the yoke on your doll for fit after the armhole row. Since it is very small, just pull it out if it is too small or too large, and start over with a size larger or smaller hook.

The pattern for the matching diaper cover will be posted as soon as I get it written up. It needs a bit of adjusting first!