You must always specify a velocity relative to something. That is to say, "it is traveling at 0.65c" is meaningless because if I am moving relative to you, its speed will be different from my perspective. We get away with it in every day life because everyone automatically assumes that when you say "I was doing 30mph" you actually mean "...relative to the ground". But note that pilots have to make a distinction between their speed relative to the air (airspeed - related to whether or not you are about to fall out of the sky) and relative to the ground (groundspeed - related to how long it will take you to reach your destination), so it's not that simple even in fairly ordinary circumstances.
Your question as phrased implies that there is an onlooker - probably the narrator - who is watching the battle from a separate vantage point. One of the ships is doing 0.15c relative to him; the other is doing -0.65c relative to him. But the important perspectives from a shooting point of view are those of the ships themselves and, as DrStupid pointed out, they both see the same thing in opposite directions. Velocities don't add straightforwardly at relativistic speeds, so it turns out that each ship sees the other coming at it at about 0.72c. The situation is symmetric.
The major problem for combatants in the situation you describe is related to the fact that the ships are traveling at sizeable fractions of the speed of light, and are (I presume) gathering information about each other using light or radar. That means that the information they have is significantly out of date, and they will have very little time to react to updates. Also, your targets are very small relative to the distance between them and the distances they travel within the reaction time of even a computer, and small inaccuracies mean a miss.