To my knowledge, there are no extant garments nor records sufficient to document any one particular approach to 15th century kirtles construction. The method that I personaly prefer however, is consistent with extant examples of medieval clothing construction. I have also experimented with other plausible construction techniques and came to a very similar overall look but found that the basic geometrical construction type is the simplest and most economic method of all. Garments such as the "Moy gown" found in a bog at St-Clare, Ireland, and the cotehardie from Sir Robert Braunches brass , English man who died in 1364, both show this type of gore settings but there are other surviving garments which consists of such a construction as well.
This type of garment was worn by all social classes throughout much of the 15th century in all of Europe. It could be worn either on its own directly over the chemise for cummun tasks or, with an additional under-kirtle (with or without sleeves) for daily wear. However, I believe that this was a garment worn as a petticoat underneath the main garment such as a houppelande or gown for mundane wear and therefor, was more of an undergarment than a decent vestment to be worn in public. For this reason, this garment needs to be fitted and supportive. For commodity and decency, sleeves could be pinned-on between tasks while worn without an overgown. There are equal amount of visual sources that shows examples with and without a waistseam.