I have a 12' bbsb with a semiplanning hull. I had an 84 Johnson 15hp on it when I got it that pushed it between 13-17mph loaded ( me, dog and gear) and unloaded( me and dog, no gear). I also used a six gallon tank ... And needed every bit of it! I got rid of that and purchased a 2008 suzuki 15 hp 4stroke elec start and never looked back! I know there is much debate about weight, torque and speed. I debated it, read every article, and lost far too much sleep than it was worth. But the two are going to be soon gone, my 4 is whisper quiet, no smoke, and the e-start is a dream.
All things considered my Johnson was 20lb lighter, but I also carried 6gallons of fuel with it versus the three gallons I carry now. I believe gas is 8.8 lbs per gallon, I am still lighter. Now I know hanging an extra 20lbs off the transome is a lot, but, my six gallon tank sat under my aft deck and I moved my new 3 gallon tank to the front. My boat does 17-22 loaded and unloaded. The boat has a great attitude in the water, not too nose high or low. Gets right up on plane, I would not hesitate to do it again.
As far as the Suzuki goes it is an outstanding motor. I would recommend their product to anyone! But then again I don't think you can go wrong with
any makers small outboard. You said yours is a displacement, I would look no bigger than a 9.9. You could probably go even a bit smaller.