The largest national % increase ever reported (data since 1960) was 12.7% in 1968 and the largest # increase was 1,938 in 1990. A 15% increase this year (and I think it'll be much larger) would mean 2,400 more murders & be the worst one year increase in murder ever recorded.
You see it in cities big and small, and I'm not counting places like Columbus (OH) that have set annual murder records but I can't find matching YTD data for 2019.