Speaker experts: Please analyse this sp-3

I was thinking that as I am only using the 15 from 100 to 800 an expensive 12 like the neo B&C that I already own may be a tangible improvement without upsetting thr apple cart of the Sp-3 box as I am adding the tl606dw subs below 100.
Since you already have the B&C 12, might as well try it.
The 12" will be about -3 dB (or more, depending on the model) less sensitive, so you will probably want to lower the HF output.