There is another big difference between improv and larp: consistency of diegesis.
In improv, players will take the scene in the direction that they feel makes the best drama / performance.
In larp (but #notalllarp), players ccare more about the deined nature of the setting and their own characters. Some larpers will stick to ‘that’s not what my character would do’ or ‘that’s not possible within this setting.’
Also, improv tend to focus on heightened / dramatic playstyles. Larp an dothis, but as a medium is naturally predisposed to naturalistic / realistic playstyles.