Greg Benage
Legend
Arcane Trickster: "Whenever you gain a level in this class, you can replace one of the wizard spells you know with another spell of your choice from the wizard spell list. The new spell must be of a level for which you have spell slots"
A Wizard 2/Arcane trickster 15 (multiclass lvl 7) has one 4th lvl spell slot. Can they not exchange one spell they know for a 4th lvl spell?
That's the general spells known rule for arcane tricksters. Now look at the specific spells known rule for multiclass spellcasters.
