which dragonair?

...15 ATK

Between those two I'd go with the 15a one. Depending on how many eggs you feel like hatching I'd be tempted to wait for a better Dratini but that's not a guarantee.

Some IV calculators list IVs as HP/Atk/Def, others as Atk/Def/Sta. From the ambiguous IVs of #2 I'd guess yours are listed attack first. But whichever order you are using, the advice to go with the 15 attack is fairly good. Ensures that you don't miss out on any important offensive break points.

don't burn through a dragonair in a mass evolution. If you're unsure, just evolve a rat and wait for a higher level/iv.

Don't waste lucky eggs on mass evolves unless you also get friendship exp for the same egg. One great friend is equivalent to 20 evolves, one ultra friend is equivalent to 100 evolves.

Assuming your Dragonairs are roughly the same level, pick the one that has 15 attack.

IF, and I mean IF, the 15 is NOT stamina, you can power up the dragonair...and once would probably be enough... for you to figure out what the actual IVs are for the second one. A 10 vs 13 stamina or 12 vs 14 will result in HP differences pretty quickly.

I once caught a 22CP rhyhorn. Could’ve been practically anything from 82-98 IV. Based upon appraisal. Was able to pinpoint it to 98 after 10 power ups.

It has been my experience that Most of the time unresolvable ambigiuty only happens with 14 or 15 stamina.

That said your comment that no matter how much you power up you can’t get clarity suggests the 15 is stamina, in which case it might be better to wait some more for a better one.