Running through a Wrath of the Righteous campaign right now, character is a Tiefling 1st level Oracle / 14th level Paladin (Oath of Vengeance, Oath Against Fiends) and I've just picked up the feat Divine Interference (we're not using Mythic rules).
Now as a pre-req for the feat you have to have a caster level of 10th or higher, a requirement I satisfy by being a 14th level Paladin (CL -3). Can I sacrifice Oracle 1st level spell slots to power the feat, or am I limited to spells from the class I used to fulfill the pre-requisite with?
Yes, you should be able to use Oracle spell slots to power the feat.