dct, hard to be more precise without a recent half (or similar) to base things on but 6.30 sounds possible. See how the 14@MP session goes if that one doesn't kill you at the end of a weeks training then you will be there or thereabouts. Without lots of 20 mile + runs under your belt, the last 6 miles will be hard to estimate.
Alan, sorry to hear about the lurgy but sounds like the immune system has been worn down by the large milage you have been putting in. At least you have got it after the race win. It's going to be 27-30C in Crete. Planning on doing quite a bit of walking and swimming which should keep things ticking over.
Spoons, that's a decent pace for your 15 miler, especially on the heat.
Westy, it will be winter before you know it. Nice intervals.