Building an Ultrasound Generator
Ultrasonic transducers are used for several applications on boats.

Alas, I haven't seen any tuned for exactly 1.5 MHz, but perhaps a transducer tuned to some slightly different higher or lower frequency will be adequate for your application:

Parsonics "14 kHz to 4.5 MHz"

Airmar "4.5 MHz"; Airmar "30 kHz to 300 kHz"

NKE Marine "4.5 MHz"