I'd agree that the jump from 15-20 watts won't be that much at all. However, some 15-20 watt receivers seem to be more powerful than others. If you are looking for a bit of a jump in power, then as mentioned, you may want to look at something in the 30-40 watt range. You are actually entering what can be a fun journey in finding a new receiver for your system. If you are up to it, what I would suggest is trying a few different receivers from different manufacturers to see which one suits your system and your preferences the best. And don't be afraid to experiment with other manufacturers!

There were great sounding receivers from smaller names as well, so don't pass them up just because they aren't part of the "big four" (Pioneer, Sansui, Marantz, and Yamaha). Also, if 15 watts seems to fill your room with enough volume, don't be afraid to try another 15 watter as well. There were some very good receivers made in that wattage range, so don't let that deter you either. It all basically comes down to what kind of sound you are looking for and what you are looking to achieve. Just try a few things. You'll learn quite a bit and you just may find that one receiver that really turns your crank. You'll never know until you try! Happy hunting!