Sorry, I didn't consider that someone might want to reset their save! If you download the new version I just uploaded, it now gives you the option between New Game and Continue Game on title screen. This new version will still be compatible with your existing save.
There's certainly things that could be better optimised, though I haven't encountered slowdown myself. What area/s gave you trouble?
It definitely wasn't just you. Looking at some of the larger rooms in debug mode I was getting around 100 fps, which is a lot lower than it should be and could easily go under 60 on a less powerful machine. Thankfully, there was a pretty obvious optimisation I could make - after doing that it's getting around 5 times the fps. Could probably still optimise further, but it should at least address your issues.
I uploaded a new version with this fix. Since there's no visible difference I also added a version indicator. As of this update, the game is at version 0.1.3.0
