15-20 minute idle time is too short, especially for an MMO.
Sometimes you have to step out real quick for real life issues.

1-2 hour timer would be more reasonable.
Remember, there's Sanctuaries in the game that's meant for people to stand and idle in.
Making the game boot ppl in 15 minutes of inactivity is ridiculous.
They're already in the process of enhancing the servers and adding more.

I don't agree with idle-booting period, but if they are to implement a system like that, it should be more reasonable. 1-2 hours.
People are paying to play this game. It's not the fault of the players that they want to remain in the game for fear of not going back in. SE are to blame for this and they have already announced that they're making improvements that should start this coming week.