The extra tenacity is coming from Hound's Tooth's crew ability, Trandoshan Barricade. At level 8- "Hound's Tooth gains 25% Protection Up (stacking) for 2 turns whenever it takes damage from an enemy's attack. While not Taunting, it has +50% Tenacity and gains +25% Turn Meter whenever another ally takes damage from an enemy's attack. Attacks that deal damage multiple times will not trigger these effects more than once. When Hound's Tooth loses Taunt, it gains Taunt for 1 turn if an enemy is Breached. While Hound's Tooth is active, Breached enemies have -25% Evasion."
I do not know where the 15% tenacity number you are using is coming from, a maxed out HT has tenacity of 58.48% as the base stat. Once you add the +50% tenacity for not taunting, HT will have tenacity of 108.48%. Hence, unless HT is taunting, you will not be able to debuff a maxed HT in the first round and it will be difficult to land on a non-maxed HT.
There are multiple different ways to beat it, but it depends on what ships you have and what ships you are facing.
