* 12-passenger van: Generally, you do *not* need a CDL to operate a 12-passenger van, even if it's used for commercial purposes (like transporting people for a fee). However, you will need a regular driver's license and may need specific endorsements depending on your state and the type of operation. You might also be subject to other regulations like those concerning transporting passengers for compensation.
* 15-passenger van: This is where it gets tricky. A 15-passenger van *often* requires a CDL if used for commercial purposes (carrying passengers for compensation). The key factor is often the Gross Vehicle Weight Rating (GVWR) and whether the van is being used for commercial transportation of passengers. If the GVWR exceeds a certain weight limit (which varies by state), a CDL will be required. Even if the GVWR is below that limit, if it's used commercially to transport passengers for hire, a CDL might still be required in some jurisdictions.
In short: You should not assume a CDL is unnecessary based solely on the passenger capacity. You need to check your state's Department of Motor Vehicles (DMV) regulations and also consider the GVWR of the van and intended use (commercial or personal). The use for commercial purposes is the biggest determinant. Contact your local DMV for definitive information.