I recommend you play around with the ebikes.ca motor simulator. It will help you see which parts of the system you would need to change and to what to achieve what you need.
For instance, if you don't have a fast-enough-wind motor or a high enough voltage to cause the motor you do have to spin at the speed you want, it doesn't matter if you have ten thousand watts available, it won't make you go any faster.
Each motor has a certain RPM for a given voltage (kV), so knowing that you can guesstimate how fast it will go for a given battery voltage.
It takes a certain amount of power to go a certain speed under specific conditions. 1500w is enough to go pretty fast (probably at least 30mph on flat ground with no headwind) if the system has the voltage and/or motor kV to do it.
Since you don't state the speed you are already able to go (as we have no way of knowing what the speed limit is where you are riding), or the speed you need to go, we can't help you figure out what you actually need to do that, so the simulator is your best bet to figure that out.
Regarding 3kw of power, unless you need to climb steep hills, pull heavy cargo trailers, etc., or go perhaps 45mph on flat ground, you don't need it and it just makes the bike heavier and more expensive.
For instance, if you only need to go, say, 35mph, it only takes around 1500w, which your system can already do, so you can either change your motor to one with a kV high enough to do that with your existing battery and controller, or change your battery to one high enough voltage to spin the existing motor that fast, and probalby the controller to one that can handle that high a voltage.
If you need faster than that just for short bursts, you can almost certainly still do the same things, as most motors can take short term loads higher than their "ratings". If you need faster speed (and thus higher power) for longer, those hubsinks and statorade would help you with that, if using your existing motor.
If you just want the power to have the power, that's up to you....but my guess is you don't need it.