Company Stock Purchase Plan- worth it ?

I invest 5% of my pay into my company’s stock purchase plan which has a 1 year vesting period before I can sell the shares bought quarterly. I normally sell immediately upon the available sell date. However, the stock is down 27% this past year and more than 50% past five years . Although the past 2 or 3 quarterly purchases have been at a low price and I always think there’s no way it will go lower just for it to rise for a few days then go back down. I’ve sold the last two to three blocks of shares at a loss and are currently down about 5% overall (-17% to +2%) even after the 15% discount. Is there any sense continuing participation in this ESPP? I’m debating whether to stop future purchases or hold for a longer period of time maybe two years