To be fair, that rule of 15 is wildly inaccurate... brewed espresso lasts a lot longer than 15 seconds

While you're having troubles with your espresso, perhaps you'd be better off weighing your dose, measuring (e.g. weighing) your drink volume and telling us the time in which it is brewed. This can be valuable information for troubleshooting and eyeballing it with a spoon isn't really the way to go.
If you are grinding and dosing appropriately the tamp is possibly the least important factor and many like the advice of "grind finer tamp lighter" for levers, but personally I don't find much of a difference with tamping pressure either way.
Stale beans are always going to be a problem and the above information can partially help figure that out.
The MCAL is reported to be capable of excellent shots; the rocky is also reported to be a serviceable grinder; but if you like dark greasy bean taste you probably have overspent for your palate...