Can I raise 15 baby chicks in an empty coop instead of a brooder? Is that too big of a space? I’m located in mid Michigan and the chicks are arriving the week of March 23rd.
You might want to divide off an area with cardboard for the first few days or a week or so. This keeps the chicks near the heat source, and provides a bit of extra protection from drafts in their specific area. I would probably take apart cardboard boxes and tape them back together to make a ring about 4 or 5 feet across, at least 18 inches tall. Once the chicks are a week old or thereabouts, remove the ring.
Something like this is commonly suggested on hatchery websites, and in books about raising chickens. Here is an example:
https://www.hoffmanhatchery.com/brooding.html
If you use a heat lamp, it is probably fine. If you use a brooder plate, there are two extra considerations:
--can the plate produce enough heat for the temperatures you are dealing with? Check the label. Many brooder plates are designed to be used at temperatures over 50 degrees, or over 60 degrees, or something like that. They do not make as much heat as a typical heat lamp bulb.
--the light from a heat lamp bulb will attract the chicks to the heat source. A brooder plate does not do this. So there is more danger of chicks wandering away and getting chilled with a brooder plate, and less danger of that with a heat lamp. Putting a small light by a brooder plate can help. Making a small "brooder" area for the first days or weeks, probably smaller than you would use with a heat lamp, can also help. This keeps them closer to the brooder plate so they do not have to run as far to find it.
After the chicks are a few days or a week old, they will enjoy having the whole space to run around, and should not have problems with how big it is. If you don't already have perches installed, you might want to do that soon: the chicks will enjoy playing on them in the daytime from a surprisingly early age, even though they will not sleep on them at night until they are older.