Try the following script and tell me if it needs some improvements:
tell application "Finder"
repeat with thisItem in (get selection)
if class of thisItem is document file then
set thisCreationDate to my formatDate(creation date of thisItem)
set thisName to name of thisItem
if not (thisName begins with thisCreationDate) then
set name of thisItem to thisCreationDate & space & thisName
end if
end if
end repeat
end tell
on formatDate(theDate) -- for example: 2015-01-01
set theYear to (year of theDate) as text
set theMonth to (month of theDate) as integer
set theDay to day of theDate
if theMonth < 10 then set theMonth to "0" & theMonth
if theDay < 10 then set theDay to "0" & theDay
return theYear & "-" & theMonth & "-" & theDay
end formatDate