Introduction:
To determine which turbine should be used to develop 1500 kW at 300 r.p.m. under a head of 150 m, we need to consider the characteristics and efficiency of different turbine types. The options to be considered are a Pelton wheel with one nozzle, a Pelton wheel with two or more nozzles, a Kaplan turbine, and a Francis turbine.

Pelton Wheel with One Nozzle:
- A Pelton wheel is a type of impulse turbine, which means that it operates based on the principle of impulse of water.
- It uses high-pressure water jets to strike the buckets on the wheel, creating a high-speed jet of water that imparts a rotational force to the wheel.
- With only one nozzle, the power output may not be sufficient to develop 1500 kW.
- The efficiency of a single nozzle Pelton wheel may not be as high as other turbine types, especially for higher power outputs.

Pelton Wheel with Two or More Nozzles:
- Adding more nozzles to the Pelton wheel increases the power output by increasing the amount of water striking the buckets.
- Multiple nozzles can distribute the water evenly on the wheel, improving the efficiency of power generation.
- With two or more nozzles, it is possible to develop 1500 kW at 300 r.p.m. under a head of 150 m.
- The efficiency of a Pelton wheel with multiple nozzles may be higher compared to a single nozzle Pelton wheel.

Kaplan Turbine:
- A Kaplan turbine is a type of axial flow turbine, which means that it operates based on the principle of reaction of water.
- It consists of adjustable blades that allow efficient operation over a wide range of flow rates and heads.
- Kaplan turbines are suitable for low to medium head applications and can provide high power outputs.
- However, they may not be the most suitable choice for the given head of 150 m, as they are more commonly used for heads below 70 m.

Francis Turbine:
- A Francis turbine is a type of mixed flow turbine, which means that it operates based on a combination of impulse and reaction of water.
- It is suitable for medium to high head applications and can provide high power outputs.
- With a head of 150 m, a Francis turbine can be a suitable choice for developing 1500 kW at 300 r.p.m.
- The efficiency of a Francis turbine is generally high and it can operate efficiently over a wide range of flow rates and heads.

Conclusion:
Based on the given requirements, the most suitable turbine option would be a Francis turbine. It can develop 1500 kW at 300 r.p.m. under a head of 150 m, while providing high efficiency and reliable operation.