I played the demo and all 15 levels were very easy, maybe too much.

Great polish, you can quickly get into the game! Well done!
for me personally the game feels a bit bland/monotone. with like the same concept (similar level structure) being repeated multiple times in between lvl 1-7.
I've got to 34/60 on Normal and dont feel too motivated to keep playing because i feel like "i've got it" and understood the game mechanics and feel like the game wont surprise me further on (it could, but not in my direct player experience).

Also, i feel the transitions between level and level buildup feel just a bit too long/too slow that it feels like waiting on the transition to complete, to play the next level, instead of it being a nice filler. them being like 20% faster (just a number off the top of my head) would improve the pacing and make it feel a bit more pleasant (transitions currently put the gameplay on pause).

In regards to the mechanics: The foundation of your game is great and the polish is good, but i feel like it could need some more gameplay mechanics that build on top of the base premise of "think logically to solve a puzzle of "how can i walk across the field"".

Idea off the top of my head:

• Lasers: There are lasers set up on extra fields the player might not be able to step on, which activate in fixed intervals and blocks all fields in the direction its pointing (until it hits an obstacle) and destroy the player if they are standing on it. 
• Building on top of the lasers you could have other synergistic gameplay elements that build off of it:
  
  • Mirrors that can bounce off the laser
  • Fields that can be rotated with mirrors on them to bounce the laser differently
  • fields that have something like a sensor, which make a nearby field walkable/unwalkable when its hit by a laser
  • Combinations of those gameplay mechanics could create more interesting situations where the basic gameplay remains the same but makes the player think differently and change up gameplay with laser death mazes with rotating mirrors
• Switches that the player has to step on to activate something for a limited amount of time
• Objects that can be pushed by the player when the player steps on a field containing an object. The object would be pushed onto the field that has the straightest path from where the player is coming from. So its trying to push straight, but if it cant, it will check for the next closest fields that are free (maybe also allow for chain-pushing). If there are possibilities on both sides, the player could be able to choose onto which field they want to push it.
  • Mirrors that can be repositioned to influence lasers
  • Objects that could be pushed onto switches
  • Bad Bombs that have to be pushed off the level to win (giving a fixed timer) or else the entire level gets destroyed 
  • Good Bombs that the player can use to remove obstacles. These bombs could be activated via various means like
    • a switch that starts the countdown
    • a switch that explodes the bomb
    • the bomb starts the countdown from the level start and the player has to figure out the best way to get it on a variable field at the perfect timing for it to explode (maybe also have a way to explode it earlier to not restrict the player to having an exact set of moves they will need. Or alternatively pushing it into the right position via chain-pushing)

So i think your game has a great foundation and a lot of potential that you could try to utilize to make it feel more varied while at its core it uses the same core mechanic for everything  (player moves and every object in the level passes on "time" by 1).