Narrowing those 15 down to one or two that are truly "friends" might help. My son wasn't able to use his stuffed animals as real comfort objects and company until he started to favor a smaller group. He now has a pooh bear from when he was a baby, that somehow became special when he was 6 or so, and 2 Build-a-Bear creations that were acquired when he was 9 or 10 and 11. He sleeps with all 3 each night and takes 1 with him (hidden in the bottom of his sleeping bag) when he goes on outings with scouts and such.
I've noticed with my kids that these things come and go, and so I don't make a big deal out of them. I always encourage them to stay in their own beds, and nudge them when they don't want to do so, but I've never been firm about stopping them. My son NEVER goes into our bed now, and my daughter, who is 8, rarely does. As long as you don't become co-dependent on it and unwittingly feed into it, they really will outgrow it or pass through whatever temporary phase they are in on their own. I firmly, firmly believe this. It's just not a big deal, in my experience.
Kids go through so many phases that can make them feel insecure for a while. I like the idea of allowing them that little extra comfort until they are through it, as long as everyone knows it's TEMPORARY.
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).