I just realized that XV broke an FF tradition that has been around since FFIV. It didn't introduce a new summon that was a former FF boss in a previous game.

IV - Mindflayer
V - Golem
VI - Siren
VII - Typhon
VIII -Brothers, Gilgamesh, and Cerberus
IX - Atmos
X - Magus Sisters ( technically Yojimbo as well)
XI - Garuda
XII - Half the Lucavi, but if that doesn't count then Chaos, Zeromus, and Exodus.
XIII - Hecatoncheir
XIV - Technically there are quite a few in story mode, but none of them are playable yet... so technically XIV broke the tradition first but I figure with enough time one of them will be gameplay ready. Money is on Enkidu

All of XV's summons are ones used before and the only boss one is a loan from XI and XIV. This disappoints me a bit because I always thought this was a clever idea by the developers and helps make some famous and not-so-famous bosses shine in the series.