Platform Builder it's quite laggy right now. It has been laggier, but even with the fixes TingThing made, still we need from our own code to be most optimized as we can.
Here are some tips & tricks:
1.- Avoid looping increases performance:
Looping decreases performance a lot, for example, when using custom huds, performance decreases a lot if we update the hud constantly. To fix this, instead, update the hud parts when something has changed it. If you collect a coin, you update the coin counter in the hud, but not constantly. I checked this and it's impressively helpful. If you use looping only when it's necessary, performace will be very better.
2.- Avoid cluttering a lot of tiles in the screen:
Tiles seems to break performance, when you use a lot of tiles and you can see 'em all within the screen.
3.- Minimize code as you can
Less lines of code easier for PB to execute them.