I have to make a luggage cake, and it has to be for 85 serving. I planing to do two tiers,the bottom tier 15"x11" 4", and the top tier will be half 7,5"x 5,5" 4". This will be enough for 85 serving?

Thank

If you are doing 1x2x4 slices (standard) that 15x11 cake will serve 75 on its own. The top tier adds another 30 so you are good to go as long as no one cuts huge pieces of cake.

HTH
Kristy