2004 MS 400 single Yanmar 6lpa-stp with 5 blade prop. Just cleaned bottom. Took it out today after replacing a cracked sea strainer bowl.
I'll post pics. Head wind but maybe 1 knot of following current.
WOT 3200 rpm 10.6 to 11 knots
2700 rpm 9.8 to 10 knots
2400 rpm 9.5 knots
1800 rpm 8.0 knots
1500 rpm 6.7 to 7 knots
1000 rpm 5.0 knots
There is no way I could come close to 15 knots. Maybe with twins and going downhill. OP said he wants min of 15. Don't see it in a trawler style hull.
I understand a 36 foot water line has a hull speed of 8 knots. I usually cruise around 6 to 8 at 1500 to 1800 rpms.