Just for an example, I'm a fan of the Running Rogue podcast, and the host, Chris McClung, is a 2:45 marathoner (6:18 pace). He really emphasizes keeping your easy runs easy, and often talks about how he does his easy runs at a 9-10 min/mile pace, so THREE MINUTES per mile slower than marathon pace. I'd say that's on the extreme end of the easy running spectrum, but it does show that you can do most of your training at a really slow pace - whatever that looks like for you - and it will be effective for training and will help you stay healthy and injury-free.