Re: first timer! 15hp.force carb flooding?
I have an 88 7.5HP Force (Sears Gamefisher) which is the same thing as your 15HP, just a de-tuned version. Sounds to me like there's a problem with the needle/seat, float height adjustment or a cracked/flooded float. I'd double check the float height adjustment. I have a factory Force manual for 9.9 and 15HP, 1988-1992 and here's what it says for the float adjustment;
With the carb upside down, adjust the float height until it's parallel (or even) with the carb's body. Flip the carb back up right in it's normal position and adjust the float drop to 5/16", this is measured from the carb's base (rim next to the bowl gasket) to the top edge of the float, measured at the side of the float opposite the needle/seat. With the float adjusted you should be able to blow into the carbs fuel connection, raise the float and it will stop the air, drop the float and air will pass.
With an outboard of that age that's been sitting I would replace the fuel pump diaphragm (fuel pump kit $3-5) and also check the primer bulb for cracks and deterioration. I wouldn't worry about changing points/condenser in your outboard as it has electronic ignition BIM's (coil packs) If one of those goes out your hosed as they are NLA, $150 ignition system upgrade needed
Hopefully,,, The guys who worked on it previously didn't mess up the carb and throttle adjustments. FYI, Don't rev the engine by the carb's throttle lever (hopefully the others that have worked on it haven't done that either) as it can bend the reeds,,, Don't ask how I know...