Wait for the flowers. I see no need to cut at this point, unless you want to delay possible flowers another 2 or 3 years.

I agree. Waiting is the best plan of action. It is afterall from seed and sometimes that can take 5-6 years.

I have a plant that I grew from a 10" cutting. It's appx 4' tall now. The first 2 years of growth it produced lots of foliage with no blooms. I only watered it with straight water. The third year I started watering with fertilizer and viola it bloomed. Used regular miracle grow and bone meal once a week. Bone meal has a high phosphorus content which is what plumeria need to bloom.