I've been drinking 15 units alcohol daily for a year and want to quit completely, what's the chance of delirium tremens and seizures i've read about? i wouldn't say i'm dependent as such?

Drinking 15 units of alcohol per day is well over the threshold of what is now called alcohol use disorder. You will need help quitting, and should seek a medically supervised program to help you get back to being healthy. Because the risk of not just DTs and seizures, but blood pressure abnormalities, insomnia, anxiety (panic attacks), psychoses etc, you should not do this alone.

Chronic excessive alcohol intake subjected to sudden cessation can create severe withdrawal symptoms, and these can vary in intensity from person to person, but the risk of DTs and/or seizures are real potentials. As mentioned, would urge a slow medically supervised withdrawal program for maximal safety.