Depends on how big the racks are, and how many you're planning to store in there. My guess is 2-3 heads. Will the freezer be dedicated to heads only or will it have meat and capes as well?
I have one of each, upright and chest. The chest freezer will fit one head comfortably and depeneding on rack sizes may fit 2, 3 would be doubtful. The upright you will be able to fit one in after removing shelves. 2 would be doubtful, might be able to but would need some sort of exterior latching on the door to keep it from popping open. If you plan on storing meat and such in it that will also take up space and limit you further
What are the interior dimensions of ur freezer? Ours is 28 cubic feet chest freezer and its 7x4x4....given ur 15 cubic feet measurement I'm assuming 5x3x3....I still think two heads is doable, given that they aren't monsters with 24" speads and 14" tines
I have a 15 and fit 2 heads. One had 21" spread and the other had long tines. It was tight but it worked.
Most freezers of this size are designed to fit through a 30" door so they have one dimension that is around 27". Depending on wall thickness you are looking at a narrow inside dimension of 23-24" the height and length inside should be greater about 32"x51".
Only reason i said 2 would be tight is rack size, lose a lot of space with the compressor and components. Been awhile since I have looked inside mine, I bet you can get 2 in. Probably take a bit of puzzle working.
A cape rolled/balled up well will fit inside the rack of basically any buck that would be taking up considerable room in a freezer, if you had two bucks with the racks together, I'll guarantee you could fit both capes between the two and fit fine. Dad and I killed 2 bucks right around 160" one year, one was 22" wide with 24" MB's the other was 20"W with 22"MB's and they would have fit fine in that cooler. Just cut the skull plate off the head after its caped and they barely take up any room if you think about.