I don't think 45 minutes is a bad time for a 5K. That's 3.1 miles, so just under a 15 minute mile, which is within the pace requirements for runDisney.
The C25K plan trains you to fully run the 5K; the Galloway method (which is what runDisney uses) trains you to interval between walking and running. I prefer the Galloway method; I can't do sustained running for that long.
The Galloway method gives you the number or seconds and/or minutes you should be doing each interval, but I don't have an app or machine to beep at me at those time frames, so I just run when I feel like running and walk when I'm out of breath. I often use the streetlight poles as goals, such as "I will run to *that* pole and then walk again."