The 2015 kia optima comes in three different audio configurations. one configuration has a navigation system, one has an infinity audio system, and one has neither. regardless, your speaker sizes are relatively consistent throughout. you'll have a 2 ohm4 inch center dash speaker, 3-1/2 inch corner dash speakers, 6-3/4 inch front door speakers, an 8 inch rear deck center, and 6-3/4 inch rear door speakers. the good news is that these are relatively common speaker sizes, so they'll be easy to replace with aftermarket solutions if you're so inclined. audio enthusiasts will love the upgradeability of the optima's head unit, and no audio system is complete without an amplifier and a subwoofer. the spacious trunk can fit quite a sub box!
The 2015 kia optima will have 6-3/4 inch speakers in both the front and rear doors. the speakers in the corner dash is 3-1/2" and the rear dash corners speakers are 8".