Well, I'd start with the manual:
Collision checks/sec (e.g. 1144 (~22 / tick)): how many times in the last second the engine had to test for a collision between two objects. Collision checks are invoked by the On collision or Is overlapping sprite conditions, and many behaviors perform additional collision checks automatically. In brackets, the average checks per tick is also shown. For example if there were 600 collision checks in the last second and the framerate is 60 FPS, the estimated checks per tick will be 10. This tells you on average there were about ten collision checks per frame, although the actual value will often vary frame-by-frame.
Thank you so much for the detailed explanations
and also, you're right, the middle of the layout has more instances of solid objects.
In this types of game (platformer), which is better:
1) put the solid behavior on the tilemap directly
2) put the solid behavior on other object (sprite or tiled background)