diff --git a/homeassistant/components/mqtt_room/sensor.py b/homeassistant/components/mqtt_room/sensor.py
index 1b4cdb1c583..4eb3a3f5171 100644
--- a/homeassistant/components/mqtt_room/sensor.py
+++ b/homeassistant/components/mqtt_room/sensor.py
@@ -2,8 +2,9 @@
 from __future__ import annotations
 
 from datetime import timedelta
-import json
+from functools import lru_cache
 import logging
+from typing import Any
 
 import voluptuous as vol
 
@@ -24,6 +25,7 @@ import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity_platform import AddEntitiesCallback
 from homeassistant.helpers.typing import ConfigType, DiscoveryInfoType
 from homeassistant.util import dt as dt_util, slugify
+from homeassistant.util.json import json_loads
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -47,9 +49,16 @@ PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend(
     }
 ).extend(mqtt.config.MQTT_RO_SCHEMA.schema)
 
+
+@lru_cache(maxsize=256)
+def _slugify_upper(string: str) -> str:
+    """Return a slugified version of string, uppercased."""
+    return slugify(string).upper()
+
+
 MQTT_PAYLOAD = vol.Schema(
     vol.All(
-        json.loads,
+        json_loads,
         vol.Schema(
             {
                 vol.Required(ATTR_ID): cv.string,
@@ -106,7 +115,7 @@ class MQTTRoomSensor(SensorEntity):
         self._state = STATE_NOT_HOME
         self._name = name
         self._state_topic = f"{state_topic}/+"
-        self._device_id = slugify(device_id).upper()
+        self._device_id = _slugify_upper(device_id)
         self._timeout = timeout
         self._consider_home = (
             timedelta(seconds=consider_home) if consider_home else None
@@ -179,11 +188,10 @@ class MQTTRoomSensor(SensorEntity):
             self._state = STATE_NOT_HOME
 
 
-def _parse_update_data(topic, data):
+def _parse_update_data(topic: str, data: dict[str, Any]) -> dict[str, Any]:
     """Parse the room presence update."""
     parts = topic.split("/")
     room = parts[-1]
-    device_id = slugify(data.get(ATTR_ID)).upper()
+    device_id = _slugify_upper(data.get(ATTR_ID))
     distance = data.get("distance")
-    parsed_data = {ATTR_DEVICE_ID: device_id, ATTR_ROOM: room, ATTR_DISTANCE: distance}
-    return parsed_data
+    return {ATTR_DEVICE_ID: device_id, ATTR_ROOM: room, ATTR_DISTANCE: distance}