Yay, in my opinion
That Rayquaza is pretty good for in-game. It's got maxed out HP, Attack and Special Attack IVs (I ran some calculations, assuming that after the Delta Episode you didn't use your Rayquaza), and although Hardy nature isn't the best it's certainly better than a defective nature.
Here are it's IVs the way I calculated:
HP : 31
Atk: 31
Def: 3 or 4
SpA: 31
SpD: 15 or 16
Spe: 16 or 17
That said, it does have very low Defense IVs (about 3-4 IVs) and a bit subpar Speed IVs (16-17 IVs). Don't let that deter you though, you've gotten pretty lucky to get full Attack and Special Attack IVs. He's worth training in my opinion, EV him to be a Mixed Attacker. But the Speed IVs are a bit low, so you would have to play around that.
Preferable Nature: Naive
Preferable IVs : 31 IVs in Speed
Preferable EVs : Currently it has the EVs gained from usage in Delta Episode, so you may want to clear that for something like this: 252 Atk / 40 SpA / 216 Spe
Hope I helped!
