M_Boats: Spinnaker for M-15

Hi, I'm interested in getting an asymmetrical spinnaker for my M-15. A sailmaker familiar with Montgomerys recommended one with dimensions of 16' luff, 14.5' leech, and 8' girth, made of 0.75 ounce nylon. Total sail area would be about 108 square feet. Does this sound about right? Sincerely, John Gonzalez M-15, Bella (628)