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No, being in a module vs. being in the main program has virtually zero effect on how fast or slow any given chunk of code will run. ("Virtually" zero because having to open an additional file may add a millisecond or two to the program's startup time.)
An individual module may slow down your program considerably, but that's because it's doing something that's slow to do. Being in a module has nothing to do with that. Putting the same code into the main program instead of a module will still be just as slow.