A few more filter images and measurements.
First is Coilcraft's P7LP filter module. These are inexpensive 7th order low pass filters (under $5 each and free samples are available from Coilcraft) intended for PCB mounting. I made a small adapter board with BNC connectors and assembled a couple dozen P7LPs in various frequency ranges to use as quick and dirty filters for tests and the like. The main drawback to these filters is the ferrite core inductors used and the consequent intermodulation and harmonic distortion if strong signals pass through the filter. I'm sure my filter board could be improved as well, but it's adequate for my purposes. As the ripple in the stop band shows, this is an elliptic design filter.
Next is a 24 MHz cutoff low pass filter used by RCA for 100 watt level marine SSB transmitters. It's all through hole parts. Looking at the response, I believe it's a Chebyshev design.
Then is an RCA 37 MHz cutoff low pass filter for 250 watt FM two-way transmitters operating in the 30-35 MHz range. No images of the inside, though, as it's soldered shut. The filter response looks to be elliptic.
Lastly is the home brew 15 MHz LP filter swept response overlaid with these three filters, 300 KHz - 1 GHz. Not unsurprisingly, the multiple stage filters show sharper transition from pass band to stop band -- that's why we use multiple section filters -- and all show spurious responses to some degree or other as the frequency increases to some multiple of the stop corner point.
Although Dave did not mention it, his 15 MHz filter and the one I built to duplicate it is a Butterworth.