you definitely have the ilevel to reforge to 15% expertise without moving gems around. Look at Tengenstein's guide here on tankspot for more info, but basically the stat priorities go like this:
Hit to 7.5% = Expertise to 15% > Mastery = Stam >> Parry=Dodge
So hit and expertise are most important, after that mastery and stam have roughly equal value and it is preferential. It's better to reforge expertise instead of gem it because you can't reforge stamina, so by putting in expertise gems you're limiting yourself. So reforge first, gem exp after that only if necessary.