You can access the FPS & Sprite counter by pressing menu and turning on “show stats” Though I find the FPS counter isn’t always reliable.
Thanks for all the support on midterms, they are not over yet but I have a quick minute to help since I think I know the issue. I had this exact problem with my boy who would be thunder game. I’m not totally sure what causes it. I do know it has something to do with loading a lot of levels consecutively (might be an extension thing). I also know you can fix this with the default “settings” extension. It lets you set variables that do not get reset when you reload the simulator. Its generally pretty useful when making a larger game like yours. Its blocks are pretty self explanatory.
Make a level “number setting” and every time you load a new level move the number up by one and use the “reset game.” Then start the player in the level corresponding to your setting. This should fix the lag. It can be tricky to implement but if the lag only appears in the boss level so maybe you could make a setting to help you reset the simulator only in this level.