In a race, I've walked faster than people running (the impact of a running was really hurting at that point, but I had the energy for a power walk), but it's the same distance and same reward at the end. There really are runners of all shapes, sizes and speeds but what they have in common is running (and walking!)
Prior to C25k, one of the big reasons I'd never run sucessfully was that I tried to keep up with my taller, leggier classmates and burned out within 2 minutes despite being reasonably fit. Being guided through the C25k podcast with Laura's instructions and appropriately paced music slowed me down to the point where my body could cope. Getting to week 5 is a massive achievement, and the progressions get proportionately easier from that point.
C25k is a misnomer for most women who won't manage 5k in 30 mins as a novice. I've been running 5 years now and have done parkruns quicker, but not recently!
So stick to your comfortable pace to complete C25k. Longer term, gently add more distance to add stamina. Then you can add shorter runs with faster sections to build speed. NHS C25k has 3 podcasts for after C25k which I still use years later. One is an introduction to intervals in a short session. Two are thresholds where the pace speeds up through the session.
If you cross-train, weights and explosive bursts of energy (squat jumps and burpees for example) build up the type of muscle that provides speed.