I do hill repeats on a 20% gradient off road, with lots of gnarly roots and mud, but it's only a quarter of a mile long. Still almost bloody kills me though! I do a 1.5 mile warm up to the hill, then do 3 reps up the hill with a jog down as recovery, then jog home. I try to do each rep quicker than the previous one. What normally happens is that I go off too fast on the first, fail utterly to beat that on the second but then give it everything on the third rep and manage it. Tonight however, I did it! Beat my first go by ten seconds and then, by absolutely burying myself on the final rep (always find it mentally easier to do that, knowing it's the last one) I knocked another fifty seconds off! If anybody saw a man on his hands and knees at the top of a hill in the pitch black wearing a head torch, breathing like he was about to die, that was me!
Hills are great training. Allows you to get a really hard workout in without the pressure on your joints of running fast.
15% over 3/4 of a mile does sound bloody hard, but I wouldn't shy away from it if you can manage it. If you do it regularly, you'll definitely feel the benefit.
When I'm on a really long training run, I have little "treats" planned for certain distances. So, I'll not start off the run listening to the podcast I have saved up (I always ensure I've got something saved like Marathon Talk or Talk Ultra) but allow myself to start listening after four miles. Then I can have my first bit of drink at mile five, followed by my first gel or blok at mile six. I then keep doing that through the run, allowing myself a bit of drink every couple of miles and a gel or something every four miles. Then, for the last couple of miles, the earphones come out and I enjoy the peace and quiet.
I don't know what brand she was wearing but a young lady at the Reading Half the other weekend was performing some warm up stretches right in front of me before the race that revealed quite clearly that she was commando under the tights.
The flip side of this is when you tell someone you're training for a marathon and they automatically ask which charity you're running for. I've had people tell me straight out that I'm wasting my time if I'm not raising money. It just doesn't occur to some people (lazy bastards mostly) that you might be doing it for it's own sake.