It's probably those ±15 pixels.
I suggest you use MoveTo behavior for the drone instead of lerp. On every tick move to the position behind/above the character. Set small values for acceleration and deceleration for a nice smooth flight.
And by the way, when using lerp you need to use delta-time. Instead of 0.005 in the last parameter, it should be 0.3*dt. Otherwise the game will run differently on different frame rates.