The 8D, 9.9D, 15D, and 20D are basically the same procedure for water pump installation. You may want to pick up a Clymer Manual (normally less than $40). I would hope it covers the water pump installation.
I always recommend the Helm, but I would not pay for a 9.9D manual from Helm..for a 15D water pump.
The hardest thing is disconnecting and reconnecting (correctly) the shift shaft.
If the manual does not say...put the motor in reverse to disconnect the shift shaft rods.
It is hard to explain where it is... hopefully, the manual has a picture.
When you go to reconnect it, position the top of the bottom nut (small nut) about 1/3 inches from the top of the rod. Then rotate the top (long) nut down to it...then lock them together. If the setting is not right, your shifting will be messed up.
Overall, it is a pretty simple procedure as long as the bolts are not corroded in by salt, etc.
Mike