not many people do not want the warranty on a new motor.

Let the dealer mount motor , set up, and prop correctly for your boat.
They will fill out all the paper work to get your warranty going
test run to make sure it is set up correctly and make sure you follow the break in procedures if they did not do it

IF a dealer gets caught selling a motor loose to a consumer, Yamaha has the option of pulling the dealers franchise.
most Yamaha dealers wont sell loose motors.
don't be cheap.
rig it with the latest gauge package.
the controls and ign harness will work.

As noted, a motor must be registered with Yamaha by a dealer so that a warranty is in effect. A dealer has to inspect the motor to ensure that all is well before he can do the warranty registration.

Are you on good terms with your dealer? Some will allow a customer to install a motor but the boat/motor package has to be returned to the dealer for an inspection. This will be between you and the dealer of course. Some will and some won't. Entirely up to the dealer.

All of the rigging stuff that was used for your 115 will plug and play with your F115. Depending upon the age of the tachometer an adaptor harness might be required if it is reused. However, as Mr. Bolt suggests you might want to upgrade to new instruments.

Are you familiar with the Variable *****ing Speed mode in the latest F115? If you want to use this you will need a Command Link tachometer. That or make up a harness and switch that will run from the motor to the dash.

And remember, there are two kinds of new four stroke owners. Those that have tried to start it when it is already running and those that will try to start it when it is already running.