This week, I have had 3 runs of around 6.5K each . The first 2 were B210K week 2 runs which were 3 x15 minute runs with 1 minute walk between - the third was 8x5 minute runs with 1 minute walk between. Essentially therefore , the third run involved 5 minutes less running/5minutes more walking.
I think the energy expended on all three runs was very similar - however, I probably enjoyed the last run the best. I can't say that I especially enjoy non-stop running, so I find even 15 minutes to be a bit painful - I can do it for a 5K Parkrun but if I am going to start longer runs, I think the run/walk strategy is more enjoyable.
Anyway, I used Runkeeper for all three runs and the average pace for each of the three was almost identical - only a few seconds per K between them.