There are people who have had very good performances, even at the marathon, without doing long runs. They're rare but they do exist. Would those performances have been even better if they'd done long runs? Possibly. But I've always thought, with some supporting information, that doing decent overall mileage is more important than doing long runs, though ideally it's not a either/or thing.
Someone else asked about your overall mileage. This is a good question. You need to have a certain level of fitness to survive and benefit from long runs, i.e, someone who runs 2-3 miles a day five times a week is going to have a really hard time with a 15 mile run while someone at 6-8 miles a day will manage and benefit from it very well. You don't say how much you run or how long you've been doing it but maybe you'd have an easier time with long runs if you ran more overall. Or maybe not.
But here's the thing, at least from my perspective. You aren't running to get a shoe contract or make a national team. You're doing it for enjoyment and better fitness. If long runs make you miserable consistently there's no reason not to scale them back to a manageable length or let them go completely.