Prime couldn't beat Galactus.
Silver Surfer would still defeat Prime. Even with 15,000 years of solar power absorption, he's still just a living battery, and he can still be shorted out like an electrical device by an EMP, or flat out drained. Any competent energy manipulator with hyper light speed capabilities could do it. I'd even say Binary could take Prime considering he still has the same weakness. He'd have to rely more on the GL ring and Sword of Heaven than his own base powers, and the GL Ring can be shorted out as well.