If you hate it then that's all the reason that you need to switch.

I haven't seen an compelling evidence that "running is not good for us", certainly not in the 15 miles a week range. Kurt Harris talks about several studies that show that active marathon runners (those who run 5 marathons or more in 3 years) have a significantly increased occurance of LGE anomolies which "might" indicate arterial damage, and others that demostrate a high rate of mortality in marathon runners.

Harris speculates: "I think that not only does sustained "cardio" not protect you from atherosclerosis, I think it is quite likely that through repetitive shear stress with endothelial damage and promotion of an inflammatory state, that it may promote atherosclerosis and/or direct cardiac muscle damage."

He also observes that runners eat the most horrible diet of refined carbohydrates possible, and that this could also be causal factor in heart disease.

1. At 15 miles a week you aren't doing anywhere near the same amound of cardio as people who are running at least a marathon a year for 3 years.
2. I'd hope you weren't fuelling 3 mile runs with lots of refined carbohydrates, because that just isn't necessary.
3. Walking is great, and is obviously much lower impact than running, but it takes a lot longer to exert the same sort of effort (burn the same amount of calories). You'd have to walk for longer to get the same sort of "benefit" (if there is any benefit at all).

None of this matters, you hate running, so there isn't a compelling reason to do it.

i vote walking. read into mark sisson's theories on chronic cardio vs moving frequently at a slow pace.

I am sure this is very individual, will just say that I've had far better results with slow movement (yoga, walking, etc) than high impact. I'm a calorie counter (not popular around here, I know!) and my n=1 research shows that I can eat more calories (which is my personal goal, I'm no longer trying to lose weight) with regular, slow movement and very little sitting than I can with the sorts of high impact activities I used to do. I've totally given up tabatas, and was glad to see them go.

I don't think it's a simple matter of how many calories the activity burns, although obviously that matters too. But for me, it seems like if I move enough (and again, spend as little time sitting as possible) my metabolism functions at a higher level.

But would not think that just switching to a morning walk instead of a morning run would do the trick -- you need sustained slow movement through the day, even if all that means is standing more than you sit, taking stairs instead of elevators, etc etc.

I used to run but it beat up my knees. I blame this on running on roads - hard surfaces and the crown causing uneven impact. Walking takes more time but is not as painful. The only big problems have been dry heels and Achilles tendon swelling. Using a walking staff helps alleviate that stress.

Why do the same thing every morning? You could cut the runs down to 3 a week and try slower activities on the other days.

I would not combine running and lifting the way you are. In my experience, the recoveries to each stress are more productive if you let your body react to one metabolic stress at a time. Definitely scale down the lifting on running days, and lift heavier or super-set on non-running days. Don't be afraid to run for longer distances more slowly, low stress.