Have any runners used HIIT to train for a race?

I just signed up for a 4 mile race in 7 weeks. I'm in good shape now but not great running shape - I can run a mile or two nonstop at a 12 minute pace. i'd like to use HIIT to train rather than classic running programs in hopes of increasing my speed alongside endurance. plus, i can only fit 2 days a week of running into my current workout program.

has anyone used HIIT to train for a race? can you tell me what you did and the results? thanks. the program i've been using here and there is the 30-20-10 5x then 2 min rest, repeat 3-4 times.