Water Pressure Question?

[RiverCityBass]

I bought an 06 ranger w/ a yamaha 150 carb new from a dealer 6 months ago. When I first got the boat the WP was around 20 @ WOT but now the WP will only reach as high as 17 but usually stays around 15 @ WOT. I asked my dealer about this and he said it was normal and nothing to worry about as long as it was above 10 I was good. Any thoughts? Is this indeed normal?

[Luke]

yea thats about normal mine runs about that WOT as long as you dont let it get to low you should be fine
they wont have much press at idle either