Which TI MCU?
SPI at 15MHz (what that controller looks to be specified for) should be able to update a 128x160 display in 21ms if you're using 16 bit color. So first thing to check would be that you have SPI running at a reasonable speed, and hopefully you are using an SPI peripheral and not bitbanging it like a lot of LCD sample code shows.
Is the MCU doing anything else other than controlling the LCD right now? If so, it's possible that the MCU is spending too much time on other things to be able to service the LCD properly, and it's a good idea to take out everything but the LCD stuff as a first troubleshooting step.
Once you've covered those things, there may be other things you can do to improve performance, like use 16 bit instead of 8 bit transfers as SiliconWizard suggests, and ensuring that you're loading new data into the SPI data register as soon as you can (usually there is a 'data register empty' flag that says the data register is ready to accept new data, and a 'transmit complete' flag that says the previous data has finished sending. You want to load the next byte or word when DRE is set, since that happens before TXC, and will give you basically continuous transmission). But none of these will make as much difference as making sure your SPI interface is performing properly.