You'd have to make a smaller size of the pattern. Figure out the measurements for the size 10 as given, then knit a sample with your yarn and needles to see how many sts per inch. Then multiply the sts per inch times the measurement to see how many sts you need, which should be close to one of the size of the pattern. This is basically 2 sleeves connected by knitting across the back, so isn't too hard to adjust.
According to the stitch gauge, the sleeves are about 8" around, so if you're getting say 5 sts per inch, you need about 40 sts. The smallest size casts on 42 sts, so you would start with that and do the incs on the sleeve as written, making the length of the sleeve the same as on the size 10 - 15½".
sue- knitting heretic