Yes...you must use all of the mana from the spawn point first.
Mage Wars Rules Book
Chapter 5-Spells-Conjurations-Spawnpoint Side Bar.
The Spawnpoint must spend its
own mana first (by removing mana counters). If the
Spawnpoint does not have enough mana to cast the
spell, you must pay the difference from your Mage’s
Mana Supply. You control all spells cast by your
Spawnpoints.
EDIT: Its only if the spawnpoint does not have enough mana, that you may pay the difference from your mages mana supply.