Lvl 1 necro spell Reclaim Energy
Reclaims the energy needed to maintain your pet, causing the pet to dissipate and restores the mana used to cast the pet times the current health percentage the pet is at (or very close to it).
Edit: extra info, this will help to reduce mana loss when summoning multiple pets.
And when you get to a lvl (says 33) quest for a mage focus item. Insta-cast reclaim energy.
For extra (fashion) points get the shovel of pons.
https://wiki.project1999.com/Reclaim_Energy
https://wiki.project1999.com/Shovel_of_Ponz