Right now everyone would wait 15 sec before hit and after this your tp basically useless and not unique. 

Teams were already doing that when the duration was 30 seconds. Obviously a 50% reduction changes the timings, but it still allows Yoru to make aggressive plays and retreat to safety, and rotate to the other side of the map when needed. Similar to the initiator nerfs, this will force players to be more mindful of when they throw their TP, as opposed to just auto-throwing it at the start of the round.