Your plight is far from uncommon.
First, the most common Leslie models 122 and 147 have 40-watt amplifiers in them. This makes it difficult enough to compete with 100-watt or more bass amplifiers, keyboard amps and drums, and if they're piped through the sound system, you have difficultly even hearing yourself let alone the audience!
Secondly, the model 47 Leslie has a 30-watt amplifier, which is even weaker than the 122 or 147. I know how you feel because my church has a 21H, which also has a 30-watt amp in it.
The best solution that comes to mind is to get that Leslie miked. A typical setup will have one microphone on the horn and one on the bass rotor anywhere from 8-12 inches away. You'll have to play with the distance so that you get good sound but avoid the wind noise of the horn and rotor. If you are playing with a bassist, then you don't really need a mic for the bass rotor, so one on the horn will do.
Also, make sure the Leslie is as close to you as possible so you can at least hear yourself. If possible make sure there's a monitor near the band as well to reinforce your sound for the band.