Puzzle : if 111 = 09 444 = 12 777 = 15 then 888 = ???

Puzzle !!! :)
if
111 = 09
444 = 12
777 = 15
then
888 = ???

Click here for Answer

One+one+one(3+3+3)=09
Four+Four+Four(4+4+4)=12
Seven+Seven+Seven(5+5+5)=15
Therefore
Eight+Eight+Eight(5+5+5)=15