Pin 15 of &gpio0 already assigned

Question

I keep getting the following error when building this file: Pin 15 of &gpio0 already assigned to 2 other nodes

[{
"resource": "/C:/Users/User/zephyr/boards/arm/pinnacle_100_dvk/pinnacle_100_dvk.dts",
"owner": "DeviceTree",
"severity": 2,
"message": "Pin 15 of &gpio0 already assigned to 2 other nodes",
"startLineNumber": 124,
"startColumn": 32,
"endLineNumber": 124,
"endColumn": 34,
"relatedInformation": [
{
"startLineNumber": 107,
"startColumn": 1,
"endLineNumber": 107,
"endColumn": 7,
"message": "Overlapping assignment",
"resource": "/c:/Users/User/zephyr/boards/arm/pinnacle_100_dvk/pinnacle_100_dvk.dts"
}
]
}]

I cannot find where there is overlap occurring.

Here is where the error is highlighted in the code for GPIO0 pin 15:

&uart0 {
	compatible = "nordic,nrf-uart";
	status = "okay";
	current-speed = <115200>;
	pinctrl-0 = <&uart0_default>;
	pinctrl-1 = <&uart0_sleep>;
	pinctrl-names = "default", "sleep";
};

&uart1 {
	compatible = "nordic,nrf-uarte";
	status = "okay";
	current-speed = <115200>;
	hw-flow-control;
	pinctrl-0 = <&uart1_default>;
	pinctrl-1 = <&uart1_sleep>;
	pinctrl-names = "default", "sleep";
	hl7800 {
		compatible = "swir,hl7800";
		status = "okay";
		mdm-reset-gpios = <&gpio1 15 (GPIO_OPEN_DRAIN | GPIO_ACTIVE_LOW)>;
		mdm-wake-gpios = <&gpio1 13 (GPIO_OPEN_SOURCE | GPIO_ACTIVE_HIGH)>;
		mdm-pwr-on-gpios = <&gpio1 2 (GPIO_OPEN_DRAIN | GPIO_ACTIVE_LOW)>;
		mdm-fast-shutd-gpios = <&gpio1 14 (GPIO_OPEN_DRAIN | GPIO_ACTIVE_LOW)>;
		mdm-vgpio-gpios = <&gpio1 11 0>;
		mdm-uart-dsr-gpios = <&gpio0 25 0>;
		mdm-uart-cts-gpios = <&gpio0 15 0>;
		mdm-gpio6-gpios = <&gpio1 12 0>;
	};
};