Depends on how it compares to the current drivetrain.

Performance between various drivetrains doesn't differ much. The gear range and realistic top speed depends on the ratios that are possible between pedal and wheel.

How smooth the shifting is, is up to the shifter, derailleur, and cassette combination you have.

Depending on the rear wheel, you could even get more gears in general, if you're replacing the entire groupset.

Generally though, nicer parts are mostly just nicer to maintain. A hollowtech II BB does perform better than a square taper BB, but the difference is a single digit percentage. To me, the main advantage is that it's easier to keep clean and replace the bearings.

If what's on there is truly just the bare minimum though, the main advantage of a shimano groupset will probably be nicer shifting.

Once you have a nice drivetrain, though, you can modify the gear range and speeds in which it works well, by switching out the cassette and/or chainring. Bigger chainring means more top speed (but harder pedaling in all gears) and a "wider" cassette means a bigger difference between the lowest and highest gears, but the jump between each gear being bigger.