I think it relates to the every manual users measurement of the experience per hour they can get in a spawn.

If you're measuring the 15min way, or count exp without refill time you get what your experience/hr is at best. If someone playing manually they may claim "Yeah I got 2kk/hr on LC". I highly doubt they refer to that being including refill time or what so ever. Not saying which is better to use, just an answer to why many people refer to exp/hr with the 15min rolling version. It's basically "how much can the bot make me exp/h compared to myself" which normally is counted without refilling time or so.

/Stusse