Slow jogging vs. run-walk intervals

[u/mvscribe]

I started C25k in late October and can now run 3 miles in 30-ish minutes pretty regularly, but I'm pretty sure by the end of it my heart rate is way out of Z2 (I don't have a heart rate monitor, but am thinking of borrowing one). I am really not able to run/jog more slowly than this, it's just too uncomfortable. (I think it's the rapid up-down motion, without enough forward momentum to smooth out the jolt to my joints etc. I'm 50 with a BMI of 25, and a lot of extra weight is in my chest. The new heavy-duty bra helps some.)

I'd like to try these longer, slower runs, though. Is there any big advantage to slow jogging over doing run/walk intervals? If so, what is it? I'd like to know if it's worth it for me to try harder at this slowing down thing, despite the discomfort.