Actually there was a thread on this subject earlier and most people agreed the 15 minutes was great to let them be able to cool down, do their thing without holding the group back.

The cooldown between smashing your head into the wall repeating content is nice and I think a longer timer would be nice to encourage people to do a variaty of content if not give people a longer chance to get things in order before their next run. Then again there is that whole "I want it now I only play 3 hours and your wasting my precious time in the virtual world" crowd as well it's just a difference of opinions.

So apparantly my answer is either A, or D whatever suits your fancy.