they are not barely top 10 these days. they are in current position because of lost points in shuffle. they were one of the consistent teams of the year.
they did't won just by tactics. they won by skill and teamplay just like astralis's team play. even when they split for the first time,they were reaching semis and finals. after that they didn't regained that teamplay and again changed a fuck tun of times.
also state of the scene was really competitive at that time. just like current top scene. now we have astralis,navi and faze solid top teams with teams like liquid,mouz,fnatic,mibr etc following them.in 2015, we had fnatic,NV,vp and tsm as top teams with navi,nip,titan,c9 etc following them.
if you get current astralis in 2015, that fnatic will beat them just like current astralis beat that fnatic in 2018. in 2018 we have peak astralis and in 2015 we had peak fnatic.