I gave a similar talk to my DH's Rotary group--definitely no quilters. I had about the same time allotted. Frankly, I think you should figure that you talk 5 min and give time for questions--either in the course of the talk or at the end. I explained that quilting involves 3 layers, stitched together. And that we rarely uses cardboard templates or scissor, instead rulers and rotary cutters (bring both); that they can be hand or machine quilted (again examples) and the difference in the time factor with each(plus I had a picture of a long arm to pass around); definitely cover cost of materials and time needed to piece and quilt one. Your quote on painting a garage is perfect. Good luck!