15 minutes is a long time between attempts. Hopefully, you won't have too many situations where you have to wait that long. Taking one or two light attempts in the warmup room isn't a bad idea if you've got an excessively long wait (like 15 minutes). I had a few meets where my competition attempts were around 140-145 or so, and I had to wait a really long time like you're describing. Going back in the warmup room and taking one or two really light attempts (like around 50%) just to stay warm isn't a bad idea. You mentioned, "and if they go light, the heavy weight in the competition attempt might be too much of a shock to adapt to" Taking a really light attempt between two really heavy competition attempts won't screw you up. It seems like it will, but it won't. You'll still be able to make the adjustment when you go up for your next competition attempt. I've done it a few times and it didn't cause any problems.
But like I said, you shouldn't have many times where this happens.