It is generally possible to operate multiple Lenovo ThinkVision M15 monitors on a laptop via USB-C if the laptop supports multiple USB-C ports with DisplayPort alternate mode or Thunderbolt 3/4. The monitors each have a USB-C connection for the image signal and power supply, but they do not support daisy-chaining (i.e. looping the signal through from one monitor to the next).

For a setup with two additional monitors, you therefore need either two separate USB-C ports on the laptop or a USB-C hub or docking station that provides multiple video outputs and controls the monitors individually. A USB-C hub with dual-monitor support can help you connect and operate two monitors.

To summarise:
- Multiple ThinkVision M15s can be operated on one laptop if it has multiple USB-C video outputs or a corresponding USB-C hub/docking station is used.
- The monitors do not support daisy-chaining, so a separate video output is required for each monitor.
- The monitors can also be supplied with power via USB-C, which simplifies the setup.

For your external setup with two additional monitors, you should therefore check whether your laptop has two USB-C ports with video output or use a USB-C hub with dual monitor function.