There is quite some trash in front of the first boss on ptr, and I don't recall it giving problems to us whatsoever (usually they have some weird ability that makes you wipe first time). But then again we didn't have to clear too much in order to reach the first boss, but there were plenty of trash mobs to the sides. Have no clue about mages, but I reckon with tank/3dps/healer it's doable.