Short fiction is a tough market, much more so than poetry, because it takes more pages. Why that matters in online journals I have no idea, but even the one where I'm an editor accept 3 short stories and 7-8 poems for each issue.

15 yes, 250 no--1 to 17. That sounds like a pretty good acceptance rate to me, for a beginning writer even with a BA in the field. It will probably improve with more experience, but other than a few big names whose works are actively solicited, I don't think anybody does much better than 1 in 7.

Craft matters tremendously. So do trends in reader interest. But persistence makes the difference in the long run. The successful writer is nearly always the one who keeps on writing.