Why even bother copying alts onto PTR to test the buffed exp gain?
I can tell you now that 15% less exp needed per level will mean you need around 15% less exp to ding per level, and that 15% more exp per quest will provide approximately 15% more exp for every quest you turn in.
Time would kinda be better spent actually leveling said alts on live where they won't get deleted in a few weeks. :x