Say my character is a level 6 Oath of Vengeance paladin, multiclassed with a level 3 sorcerer (of unspecified subclass). At level 6, paladins do not have access to 3rd-level spells.
The character's total level is 9, so does the character have the spell haste automatically prepared, given by the Oath of Vengeance's Oath Spells list at level 9? Or is that level requirement meant to be paladin levels?
The Oath Spells section of the paladin's 3rd-level Sacred Oath feature says:
Each oath has a list of associated spells. You gain access to these spells at the levels specified in the oath description.
The "Oath Spells" section feature below each subclass clarifies:
You gain oath spells at the paladin levels listed.
As a level 6 Oath of Vengeance paladin, you only have access to Hold Person and Misty Step as your oath spells. The rules for combining spell slots for multiclassing have nothing to circumvent the limitation set by the rule above.
All level-dependent features in chapter 3 (Classes) of the 5e Player's Handbook are dependent on class level unless otherwise stated.
All level-dependent features outside of chapter 3 are dependent on character level unless otherwise stated.
You would use class specific level. You get oath spells the same way you get class abilities, via class levels. Therefore a Paladin 6/Sorcerer 3 would act as you are a level 3 sorcerer (only sorcerer abilities up to level 3), and a level 6 paladin (only paladin abilities up to level 6).
