is it true you can re cone a sa sub from a 12 inch sub to a 15 inch sub if so how is this possible ?

New basket and softparts. Yes it can be done. The motor size stays the same throughout all the sizes.

You just change the basket from a 12 to a 15.

You purchase a 15" basket and a recone kit for a 15" driver. Remove the motor from the 12" basket, install on the 15" basket and install the recone. Done.

really that is something else . i got a question i never own a 15 before just 12's and i been thinking if my 12 inch sa ever goes out i was thinking about re coning to a 15 but i am not sure if i should do spl or copper for daily. and another question would a 15 take the lows a lot better then a 12 will or are they about the same ?

The lows will be louder and so will everything else if you step up in cone area

It won't "take the lows" any better or worse. The coil question will depend on how much power you plan on using.

well i have 2 amps both are 1200 watts each and i am running 1 right now at 700 watts so if one is good enough great but if i need to use both i'm ok with that.