There are too many variables to give you an accurate answer at this time.
You may go to the Evinrude.com website and look up performance reports for pontoon boats for a 150 HP and if your boat is not listed, find one that is close to the weight and size for an aproximation.
By the way, welcome to the Evinrude family.
-- Travis McGee, main character in a book series by John D. McDonald
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.