Hi,
the reason for big footprint for Hello Word application is that there are several IO drivers are enabled(installed) in MQX BSP by default.
You can simply switch them off in user_config.h (e.g)
#define BSPCFG_ENABLE_GPIODEV 1 -> change to 0
#define BSPCFG_ENABLE_ADC 1 /* NOTE: Shares wires with I2C1, SPI0 */
If you need optimize even more , you have to create your own size optimized drivers (or modify current ones). THe MQX drivers are designed as an generic abstraction for the peripherals modules, portable across various processors making available as much features as possible. There is always trade of between code size and features + portability.
PetrL