Bucking most of the advice in this thread, I lean towards what CLDave said above with you being on a smaller lake. In that situation I’d likely go SPS/115 instead of EPP/150. I did water test out a few 115HP’s tritoons when ”shopping” in 2016.
On a smaller lake, I think the improved buoyancy, ride, handling, and getting up on plane quicker than dual toons or EPP, are important factors for choosing the SPS. On that smaller lake, you wont have the same ability to utilize the extra 35HP with the 150 anyway, so why not compromise and go for a better ride?
From water testing in 2016, with 3 adults, light fuel and no other weight on board my test runs were regularly low to mid 30‘s MPH with the 115 tritoons. Now, I had a budget to go bigger, and ended up with a 200HP tritoon. I never water tested one loaded down with weight and people, so I cannot speak to that. My guess is you probably will notice the 115 being impacted the most when loaded down with weight WHILE turning during towing people on tubes. It will bog down then, but on your smaller lake might otherwise be just fine for your uses. The 115 performs markedly better on a tritoon because you get on plane quickly with the SPS hull.
This said, if there is anyway to trade off some options, and squeeze your budget up to a 150 with SPS as many others have suggested, you absolutely wont regret it. With an SPS/150 you have NO limitations at all, better future resale value, and if you trailer to other lakes, will be able to really utilize the boat to its fullest potential. Of course that’s easy for me to say with your money. You want to try to get the last boat first, but you don’t want to do anything foolish financially either. Always a tough decision when boat shopping. So much to consider, and so much to “want”.