I need help with my mercury 15 hp 4 strokes engine. It leaks pretty bad. I thought it was fuel pump or carburetor or clogged jet but turn out it just leak.

The engine started fine when I first prime the bulb to get gas to engine.

Disconnect the gas supply tube and I see a lot of gas shooting out while engine running so I guess the fuel pump is fine too.

here video of the leak, not sure what part or gasket I need to fix this leak.

 

 

Its the gasket for number 27 on your diagram. You can either order a gasket through Mercury or go to the auto parts store and get a roll of make a gasket material. 

Thanks, but I think I know what part I want but still not sure how I can handle it. It part #25 Diaphragm and #24 seal. The part #24 have been leak a little of gas for a long time ever since I got this boat. My friend tried to fix this problem but I guess he didn't get the right part for it.

Now my another problem is, if I have mechanic fix this, it gonna cost me 150 - 200 included $25 dollar parts. The whole new carburetor kit will cost me around 200 and I can change that myself easily. Decision decisions ???

If you are not really good at doing engine repairs take it to a qualified mechanic. You could make a bad situation much worse.  Fuel leaks and hot engines mix very badly.