Quality renders take longer to render. That's unavoidable.

What do you consider 'long'? For me, I try to aim for less than an hour for a render. You may think 5 minutes is too long...

What version of Poser, what system specs do you have? CPU, RAM and OS all have an impact on what can be done and how long it takes. GPU, not so much.

How much of the image will the water occupy? What else is happening in the scene? How big is the render? Is it indoor or outdoor? All these impact render times.

The quickest way to render an ocean is to use a mesh (waves modeled) and add a glossy material to the surface. You won't be able to see through it, but it will render fast. Lots of video games do this, and Silent Hunter 4 had the option to turn the water transparency on or off.