i dont know much in this field but i just have a few words for you.
try to find out whats the RMS power of each of your subs/speakers and if you want to run it 2 or 4 ohms.then buy an amp that has enough power to feed your subs/speakers.if all in all lets say you have 500 RMS each sub/speaker and if you have a two then thats 1000 RMS,so you need an amp that has 1000 RMS.its up to you if you want 2 or 4 ohms,as long as your amp has the pwer to push both your subs/speakers.if you install it and notice that your lights dim when a loud bass hits,then yuo might wanna consider either buy a separate battery,replace more powerful alternator or a capacitor.but usually a capacitor will do.
hope this helps you out a bit.good luck rattling your ride.
also choose for the proper wire gauge.if you have a powerful amp you need a thicker amp cable.so as the amp to subs/speakers cable.avoid mounting your amp on your subs' box,its not reccomended.place it where air can circulate or somewhere cool.w/ or w/o the a/c turned on.but its still all up to you where you want your amp/s to be placed.
2 15"? You're going to put it in the civic trunk? hmmmm I dont think that you'll be able to fit the 2x15 enclosure in your trunk. The enclosure space for the subs are really important to get the correct sound. I'm guessing you're going to need 4-5 square cubic feet of space for the pair. Are you going ported or sealed? If you top this off..its gonna pound.