There is a point in the Dawnguard questline when you just have to take a break because you're still too weak to take on not one, but two revered dragons.

My character is currently lvl 22, wearing steel plate armor, which has an armor rating of 90 (115 with helmet).

I'd probably die in one Fire Breath attack.

Yeesh. I'm on level 35 still wearing the Thieves Guild armor and I don't think i'd take on those and my armor rating is 190ish.

i took them down at lvl 16 with a full steel armor with aprentice lvl they are quite easy

True Nords don't fight them above level 5!

What difficulty are you on? I did it at 30 something my first time on master, and it was a really tough fight (fun though. Beat only by Miraak in my opinion). It didn't help that I was still a vampire at the time so the flames hurt more and my health didn't regen. Come prepared. Bring some fire resistance equipment and a good weapon. If you're properly equiped, 22 is definitely manageable so long as you're not playing on Legendary.

It depends on your Magic Resistance.