Thank you. You're not the first one who says it's a bit slow, when I first heard it, I made a joke that it's because of years of practicing meditation and playing chess, which might make my perception of what's slow a bit off :-).
The pathfinding is done entirely by Unity, I just cast ray from screen space on a position where the player clicks to world space to tell the NavMeshAgent where to go on the NavMesh.
I noticed your game is also made with Unity. I wrote some blog posts/tutorials on GameDev.tv Blog about Unity. Maybe you'll find some of them useful: https://blog.gamedev.tv/author/marian/.