The Original Nexus 7 is an incredible device in it's own right, but it has struggled in the flash memory speed since its release. This has only gotten worse in these devices over time as the devices have aged. The 4.3 update which added TRIM helped with this a bit, but the device still suffers overall. Developer "legolas93" has built a custom kernel with F2FS to fix the situation. F2FS stands for (Flash-Friendly File System) which was built specifically to take into account the characteristics of NAND flash memory based storage devices. F2FS improves IO speed on the Nexus 7 2012. You will have to first format your memory meaning you will loose everything. It is recommended that you first backup your phone and load the backup to your PC so that you can restore it later. You will need to flash the specific TWRP that is modified to work with F2FS. There is full install instructions and all the files you need at the link below.
Via XDA