If you used a single decoder (or several smaller decoders acting as one) then you can only turn on one LED at a time. If thats all you wanted to do you just need 15+7 pins (connected something like this: )
Since only one LED in each bank is going to be on it could be accomplished with seven 74xx154 4-to-16 decoders (one for each bank) or you can wire it as pictured in the above and strobe each LED that you want to be on for 1/7th of the time with 7x the current. If you do this fast enough it looks like they are on constantly (this is what is often done for marquis displays).