Hi and welcome!
At levels 40 and 56, Spellhowlers get the “Fast Spell Casting” passive skill levels 1 and 2 respectively, which lowers their casting time (without increasing casting speed). Those skills works 100%. Are you talking about this skill?
Also Karmian set (Tunic, Leggings and Gloves) and Homukulus’s Sword with Acumen SA should increase your casting speed by quite a bit as these sets also work. Also make sure you buy a potion for casting speed from Trader Woodrow called “Greater Magic Haste Potion”.
Your casting speed is the lowest compared to Spellsingers and Sorcerers, so also keep that in mind.