wah in 5 months u cut down 2 mins plus. That's insane. I can only run 8:50 after years of training and even then only at Maju where the distance I highly doubt is 2.4You need both actually.
Intervals to build up your speed
Long run to build up your aerobic capacity.
When I resumed running this year,my 2.4 was close to 11 mins. Now it's at 0850. The most effective way in my opinion are "controlled intervals" whereby you are pushing and still be able to complete all the sets at the end of the day.

