Overview
ST AR-15's Mod comes with a few benefits:
Her Skill 1 gains 5% extra RoF, pushing her up an RoF bracket at level 109. This is also true with her Night SPEQ.
Her Skill 2 is an extra hit of 10% Damage, which can Miss, Crit and is affected by Armor like a normal attack. This makes her slightly more effective against linked targets as link protection will be less of an issue.
Her tiles also gain a small increase.
Her Mod III SPEQ gives 15 Damage and 30% Crit Damage plus some Accuracy, quite nice.