HI Norris,
Not a problem.
As you know, more speakers get destroyed by clipping than by overdriving.
Tube amps of course clip more gracefully, but they also clip a LOT more, if they are low watts.
I am not sure if the difference between a 15 watt abnd a 20 watt amp will justify the search, the 20 watt will clip 1 to 2 db higher than the 15 watt, but that's about it. I doubt if he will melt the Jordan with a 200 watt amp, unless he drives it at high watts rms for an extended period, at which point the user would be TRYING to wreck the driver. THe old Carver amps, like the TFM-45 were built to replicate some of the tube sound with an output impedance of 2-3 ohms. Or you can just put a 2-3 ohm resitor in series with the amp & driver, to get some of the tube sound.
Just my 2 cents.
-akhilesh