Did 15 year olds used to marry?

from roman times to 1927 the age of consent was 12

and in the Old west a 13 year old Girl was almost an old Maid unless the Family had Money

in the UK gentry 14 year old Girls dressed to find Suitors

Up to 12 the Girls wore short dresses showing their Pantaloon's the under ware with layers on each leg

at 12 it was classified as Immodest

Victoria and Albert Museum in london it shows the dresses for all ages

Ya because the way of life demanded it. Since half of newborn did not make it pass their 5th birthday, you needed to produce a lot of babies to insure the continuity of the ancestral tree. Back in those days, medicine could only take you so far and doctors did not have the cure to most sicknesses, so depending on your lifestyle, you could die in your late 30's or 40's, though more prominent lifestyle got you one or two decades extra.

Lower class and new settlers would benefit from an early marriage. One, young teens are more likely to get pregnant, in fact it is pretty much in their prime. So you would want your 18 or 17 year old son to marry a 13 - 15, year old girl. Lets say you live on a farm, back in those days it required a lot of help, so large families made the task easier. Building a colony is hard with just 50 men, so if everyone had 1-2 child you would have a maximum of 80 men. A bit of extra help but not much of an improvement.

So yes, it was common practice but it was also an adaptation to the realities of life. If peasants died in their 30's but got married in lets say 25, you might have had 2-3 children by their 30th birthday. If half the kids never made it out of infancy, when the parents died there could very well be only one kid left, the mother might have died in childbirth and the father is now blind. This kid now has to take care of a sick father and 5 acres of farm land. It was better to have an early start than to have a late start and gamble on how many family members would succumb to diseases.

yep, back then when a girl would get her first menstrual period and was thus able to have children, they were also seen as being able to marry. Many girls, ages 11-12 were married. More often than not to men in their 30s sometimes older. Pedophilia is relatively new, in modern these modern times where most people don't marry until at least their mid twenties. We have came a long way haven't we?

You did not specify country. In other countries this still occurs with some beign married at birth (although they do not live together till much later) but as for confirmation my grandmother was married at 15 and so was 4 of her siblings. My aunt was married at 16 but most girls were often married between 16 to 19 with males normally being in their mid to upper 20s

Yep, sometimes even younger. It's illegal now for good reason.