I hate trying to coordinate a meeting with more than one person. I've since stopped having my "annual xmas dinner" because it was SO painful to get 6 people to agree on a date.

I also don't put a lot of effort into arranging meetings with friends because they never seem to bother. I do think it should be a two-way street in both sides making the effort, not just one.

I'd say if there's a pattern and you feel like like they're doing some background work in avoiding you, I'd say let that go. It's a shame to let a 15 year friendship, but I recently ended a 20+ year friendship because it was just too difficult.