Thank you for the answers guys!

Due the fact that my DRK is already lvl 55 I ma level him up to 60 and maybe gear him up abit and doing some Endcontent stuff before leveling WAR - but not sure yet.

A friend told me that once you have a char at level 60 you get Bonus EXP for your alts up to level 60, is this true?
If yes, how long does it approx. take to get a char from level 15 to 60?