I am a big fan of heat plates over lamps personally. Chicks need access to warmth but ALSO the ability to cool off as needed. Plus, heat plates (or the DIY version with a heating pad, which is what I actually use) allow it to get dark at night. Which just seems nicer for the chicks. Mine all have gone to bed and slept all night (SILENTLY!) using a heat plate.
I suggest building your setup and testing it out with you there to observe. It’s pretty easy to see and hear if the chicks are happy. Quiet peeps and twitters are good. “Car alarm” urgent cheeps mean something is wrong in their little world. As long as the space is free of drafts and your heat plate is large enough and rated for lower temps (brands vary), the heat plate should work great.
Another option is to keep them indoors in an old packnplay. I recommend putting a crib sheet (not a pack n play sheet - one for a crib) over the top to keep anyone from hopping out as they grow. That won’t get them all the way to 6 weeks though…only about .5 sq ft per bird with 15. So you’d need to find two that are cheap enough to “sacrifice” to fit all 15 if you go that route. They wouldn’t be fit for a human after this

. And if you have two, you’ll need to reintegrate the flock later on

.
Anyway, maybe some of those ramblings are helpful.