well.. the tens each have 68.05in^2 of effective cone area, totalling 136.10in^2
the 15 has an effective cone area of 163.70in^2.
youll have more come area witht he 15 (louder). the 15 also has a higher sensitivity, so even thought the two 10s combines can take a little more power, i think the 15 would take them in SPL regardless.
so if you want loud, go for the 15.
the 10s might be a little punchier, have better transient response, and sound a little better with rock music, where as the extra LFE the 15 will offer will prolly make the lower noted rap songs sound better.
10s might also be a little easier to fit in the accord.. i found that its generally easier to fit 2 small woofs side by side than it is one big one in the middle. but you should be able to fit a 15..
if you cant fit liek 17 inches high in your trunk then i dont think i would suggest it. you sould almost definately fire whatever combo you get towards the rear of the trunk though, so dont say you can fit the 15 and then fire up into the rear deck.
its all a matter of preference man.. but in short, the 15 will eb louder