I've been thinking about getting the 522 VP pants, also using the 502 shoulders I got, and maybe getting the 522 helmet as well. However, I'm not quite sure if that would warrant losing the T14 4p bonus.
Could somebody give me some input on it? Would appreciate it.
Honestly? If the tier pieces you have were twice upgraded heroic pieces (level 517) there might be a debate to be had. The stat upgrade from 483 and 496 is absolutely huge, just by swapping out the helmet for a 522 you'd be getting about 800 stamina (~20k life) - the T14 4set was mediocre at best and when compared to the amount of health that those three upgrades would give you fades into insignificance.
Don't worry about the T15 bonuses either, the 2-set isn't particularly compelling for anybody and the 4 set is only really useful if you are in 25H content and your DPS all have their bonuses.