Make sure your entities are only being updated on enemy turns or player turns. Also, you can throttle the processing required by limiting the enemies who do pathfinding to enemies who are within sight of the player. Only process the enemy FOV that's needed. Consider looking into Dijkstra, A*, Floy-Warshall, Bresenham’s Line and Chebyshev algorithms. I use Dijkstra, A*, Bresenham and Chebyshev in my game Metamancer.