Beta 15 and Delta 15 are not musical instrument speakers.
they are designed for mid bass drivers in a PA system
and need to be run on a highpass filter to keep bass frequencys to destroy them.
Otherwise as a fullrange musical instrument speaker they will handle no more than 40 watts below 100hz
I think your using the delta in your portaflex Jimmy, and it might work fine with a 35 to 50 watt amp, otherwise wont work well at all in a highly powered 5 cubic foot box like the 115e.
The TS calculated sensitivity of the beta is horrible at 95dB
the Delta a little better at 96dB
The cast frame
Eminence CB158 Legend at 98dB is the affordable go too driver.
and is most likely the speaker Ampeg is using.