The placard in the boat, does not tell you the weight of the boat.
Also, not all placards contain the same into, as they have changed over the years, and from manufacturer to manufacturer.
All outboard type boats will list the maximum hp that can be used.
Some will give a maximum number of people and their weight.
Some will list maximum weight of people and gear.
Some will list the maximum weight of people, gear, and the motor.
None that I have seen, will tell you how much the boat itself weighs.
You need to reference a manual, brochure, or nadaguides to get the hull weight.
So, hull weight,
plus full fuel load weight,
plus batterie(s) weight,
plus motor weight,
plus trailer weight,
plus miscellaneous gear weight,
plus cargo in tow vehicle,
If you tell us what rig you are looking at, we could give you a guesstimate of the total weight.
Make, model, year of boat and motor would be helpful.
You might be able to squeak under the 1500# tow capacity IF it is a more basic aluminum boat.
Also, check not only the tow capacity of your vehicle, but also look in the towing section of the owners manual, and see if it requires the trailer to have brakes.
Many vehicles with a 5000# rating, require trailers of 1500# to have brakes.
Also, your state towing laws may require you to have brakes.