Yes

i thought the mechnanic was if he hits you for 10k, you get 10k and the enemy 8,5k?
so.. i take 15% damage when the buff is on? ._.

You don't take the full damage, it reflects back the percentage of damage.

oh i see, thought it could block and reflect the damage, was not thinking about it properly

i was thinking in the skill because spiked scales seems like a huge buff but you eat the whole damage anyways
when im in the bf, (since i have no damage yet) i try to stunlock people but most times i just cant reach them

Having a skill with a shield layer and reflect doesn't really make sense tbh, because the shield layer would stop the next incoming damage so there would be nothing to reflect back. 100% reflect would stop you from taking any damage anyway, because 100% of it would be reflected back at the attacker.

The skill as it stands is actually quite powerful if used at the right time in PvE but not so useful in PvP since it's impossible to know what skill a player will use on you next in most cases. PvE tho, you just use it when a monster is casting a big skill and reflect back massive damage. Making it 100% would be very overpowered - you could just stand there when for example, Arcturis casts his OHKO skill and reflect all the damage back at it.