My son is also 15 weeks and has also been waking up earlier for a feed despite having gone to 3am in the past. I was also assuming it was a growth spurt but it has also gone on pretty long.... now into its 6th day. Do growth spurts last that long?? He is clearly hungry when he wakes because he takes a full feed both times (2 and around 5.30am). ALso, I had moved him to a 4 hour EASY but he got really hungry and unsettled so now I am back to a 3.5/3 hour EASY. The only things I can suggest for you are:
* when you cluster feed.... what time is the feed before 7pm? Maybe if you have that feed earlier it might help with the 7pmfeed? Or maybe give the feed at 7.30pm instead? The other thing might be that maybe the cluster feed is not working for you so you could just merge those two feeds and feed at 6.30 or something like that.
* When he wakes, are you able to resettle him at all? Does he take a full feed each time?
*Maybe if you shortened the time of the 4.15 am feed, he might be more inclined to feed well at 7am.
what I am doing is trying to resettle if he wakes, if that doesn't work within 10 minutes, then i am feeding him. Its frustrating because it has gone on so long and I don't know whether it is a growth spurt or not. He is also feeding well during the day so I can't see how I can up his intake there. Lets hope for both of us that it is just a growth spurt and that they will settle down again soon.
Good luck
Jacqui