If the answer is not 15 then there must be some restriction on how many stickers must be on each piece of paper.
If papers are allowed to have 0-8 stickers then there are 15 ways to place them if only the number of stickers per page matters.
Maybe the pieces of paper are actually distinct, you just don't care about which stickers are on them.
In this case there will be \(\dbinom{11+3-1}{3-1} = \dbinom{11}{3}=165\) different arrangements.