Judging from this the map_update_interval is set quite high. This may lead to slower map updates.
Does your odometry give you reasonable movement data? In general GMapping updates the map after some minimal translational or angular movement of the robot. This is controlled by the linearUpdate and angularUpdate paramters. (See: GMapping parameters) If no movement is detected (by the odom -> base_link transform), no new scans are integrated into the map.