I dont play on neltharion so can't really say for sure, but I doubt Neltharion population is as much as/close to as much as Icecrown population, even if u take away ppl on log in screen etc. and while top15 would deffo be better than top10, rag and dw each had top15 first season when population was like 4-4.5k online at peak time per server, so I still think top 20 would be more fair since that would only equal the same as before seeing as Icecrown is a merge between 2 servers.