Mercury upgrade

Just acquired a 2006 mercury 15 hp 4 stroke 20in shaft
i know there are carb kits and bigger carbs u
can install to get more power. Is it possible to upgrade this motor?
and also this mite not b in the rite topic area but I'm lookin for a boat
for this motor if the shaft is 20 inches how tall does the transom need
to be for the outboard to operate properly?

The 15 horse was already the max horsepower you could get from that block unless you are a motor builder and completely reworked it.

The 20 Merc has a design all of it's own and was engineered/built as a brand new, stand alone model, so no "bolt on options" to turn a 15 into a 20.

And if you have a "long shaft" motor (20") it's designed for a 20" transom (although different boat models may not be "exactly" 20" in transom height, they are generally within an inch either way.

You can put a long shaft motor on a short (15") transom. It will however, create a little more drag (but this is only a 15 horse, so minimal). The biggest (potential) issue would be that fact that you have 5 extra inches of "stuff" down below the hull so you would have to be mindful that you didn't hang it up in very shallow water.

There are commercially available jack/elevator plates that go the cutout of the transom to add the inches you need to mount a long shaft at the correct height, but it does (obviously) elevate the powerhead etc 5" higher which may or may not be convenient (higher reach if it's a tiller) or cables elevated if it's remote - but it works fine otherwise.

Thanks I think u answered all my questions and if 20 in is a long shaftThis must b a 15 in cause it's short just trying to find out some info beforeI buy the wrong boat and it won't work rite

A 15 would be more typically a short shaft (15" although long shaft are absolutely available) - far more common in that model which was primarily designed to power 12 or 14 foot utility boat.

I run a 15 horse on a 14' utility that had a console added (so steering/windshield). The weight of the unrigged boat was a "fairly light" 220 lbs. Add the motor (75lbs - 15 horse 2 stroke), safety gear, anchor and a few odds/ends, it's rigged weight on the water is about 400 pounds.

Add myself and the wife (310 pounds - 200 of it is me ) and I see a top speed on calm water/no wind of about 22 mph - pretty good for a small motor.

So that may give you an idea of the type of performance you could get at the "top end" - if I add 2 fishing buddies the boat is lucky to make 17 mph with 15 being more of the "full tilt" potential under ideal conditions.

The only sure way to get more power out of a 15 horse merc, be it 2 stroke or 4 stroke, is to sell the thing and buy something bigger. The 15's are at the top of the game for the block they were built on.