How to correctly set publishing rate to prevent lag?

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I am experiencing lag when publishing markers in a callback and am unsure how to resolve this. When my node is started, it publishes at a similar rate to which it receives data from a subscribed topic in a callback. However, after a minute or two, the publishing rate drops dramatically and is out-of-sync with the data subscribed to. This has been shown using rospy.Time.now(). The code I have is as follows:

class Example(object):

    def __init__(self):
        self.sensor_sub = rospy.Subscriber("sensor_data", Int16, self.sensor_callback, queue_size=1)
        self.marker_publisher = rospy.Publisher('visualization_marker', Marker, queue_size=100, latch=True)
        self.sensor_data = Int16(0)
        self.pose = PoseStamped()
        self.marker = Marker()

    def sensor_callback(self, sensor_msg):
        self.sensor_data = sensor_msg.data
        self.get_pose()
        self.pub_marker(self.pose)

    def get_pose(self):
        # SOME CODE TO GET POSE (self.pose) #

    def pub_marker(self, pose):
        # SOME CODE TO DEFINE MARKER #
        self.marker_publisher.publish(self.marker)


if __name__ == '__main__':
    try:
        rospy.init_node('test', anonymous=True)
        Example()
        rospy.spin()
    except rospy.ROSInterruptException:
        pass

Any ideas how to solve this lag problem?