14' Valco 15 HP Evinrude prop suggestion

First post here. I have a 14' Semi v with a 1977 15hp 2 stroke Evinrude. Primarily used to kokanee troll on reservoirs in California but I want to use it to get in to some duck hunting spots on slow small rivers. Contemplating getting a small longtail for it but most of the waters I might use it in my outboard can probably get me in to 90% of the spots. It currently has a 9.5" x 10" 3 blade on it which has seen better days. I'm hoping to get a little more top end for scooting around the reservoirs between fishing spots so I will probably get another 9.5" x 10" or maybe an 11" pitch.

For shallow water river stuff I was thinking maybe a 4 blade 9.25" x 8" might be good to hop up on plane quicker. Don't need the top end speed but staying up with a heavy load would be desirable.

Never really played around with prop style or size always stuck with the stock recommendation. At $70 for an aluminum it won't kill me to experiment a little bit. Any advise would be appreciated.

I have a 70's 15 hp Johnson. I had a prop with a pitch of 10 witch was running around 5400 rpm so I tried a prop with a pitch of 8. The rpms went to about 6200. Yes I did gain a few extra miles, but it also increased the noise level so much that I switched back to the original prop.

Running the stock 10 pitch prop I'm getting 5050 rpm at WOT for 15 mph with myself, two kids and fishing gear. That's around 25% slip! Going to order the 4 blade 8 pitch tomorrow and see how it works.

Afraid I'm overworking my motor running it that inefficiently at low RPM's. Might not increase top end but I would not be surprised to see some increase just based on how poor the current prop is performing but hopefully see more consistent performance between light load and a heavy load when my brother decides to tag along.