The single best upgrade to make a bike faster is tire selection followed by tire pressure choice with the chosen tire.

Weight is entirely dependant on the bicycle's design for intended use. A touring bike will be heavier than a road design optimized for speed. Unless you are lifting and carrying the bike multiple times a day, the bike's static weight is not the primary deciding factor for a good riding experience. Any bike can feel "fast" if you run the right tire and gear it appropriately. Far better to get the tires, then figure out your riding style and natural cadence. You will only find this out by riding enough miles.

Then figure out if the gear spacing is working for you for your type of riding, your natural cadence and your terrain. Change the gearing to fit these variables appropriately. Once you do, the bike will feel live, responsive and an extension of your body in covering distance. That's when the fun *really* begins.