Re: Motor swap
Like stated earlier, not sure what the trim issues are, but downsizing a motor in my experience would make the trim issue greater as you are dealing with 30% less power, pushing a smaller prop, and paying more attention at maintaining speed.
Example, I had a 14 foot aluminum with a 25hp ran good but took a while to plane out (relative to the motor and hp I was dealing with) I hung a 40hp on that boat, while the 40 weighed more I planed in like 3 seconds.
Another example, my current rig came with a 70hp Johnson, it took a lot of trim work and maybe 6-8 seconds to plane, but over all decent performance once moving. However frustrating the amount of work it took to dig out. So I repowered and maxed my HP at 115. Its night and day drop the hammer and go, I still trim the motor but I the rig isn't nearly as sensitive to being at the correct spot in order to plane out.
I think it would be a terrible mistake to unbolt that 150 and hang a 115 on it. For a beginner it might seem like a lot, just don't drop the hammer, you do not have to run the motor WFO go half throttle, build your confidence slowly and by mid summer you will be perfectly fine and comfortable.
If you do not follow my advise (do what you like) at least entertain this thought. Buy good used 115, hang it on the boat and run it but DO NOT sell the 150 YET wait a season or so. Because you might find you do not like the 115 and all you would be out is a weekend to switch it back. If you sold the 150 to buy the 115 there is no getting your good motor back in the event you are not happy.