There have been various improvements to this over the course of FS Traffic's updates; however, it's sadly not something that can be removed entirely without affecting the traffic generation at the destination airport.
The small freeze is caused when the FS Traffic module detects that the player is within a certain radius of the destination airport, and starts to read the schedule files that are stored locally on your PC. Once it reads those schedule files, it'll start to generate the relevant traffic. The more schedules that exist at the destination airport, the longer it'll take for the FS Traffic module to read those; therefore, the size of the freeze is directly related to how busy the destination airport is. For example, if you approach a small to medium-sized airport like Manchester (EGCC), you may only notice a small stutter, but if you approach Chicago O'Hare (KORD) at rush hour, you will get a larger stutter.
Mark - Just Flight