Hi Alex,
the SDK documentation does not contain details about the timing, so let me share documentation for previous standalone version of the drivers - attached. Take a look at "5.1.1 Initialization/Read/Write Timings". MPC5775K is relatively close to MPC5775E, so we can use this one as a reference. This is the timing for three 16KB blocks. As you can see in the table, worst initialization timing is about 100ms. Because the erase time of 64KB is significantly higher:

... and because you can have much more data there, it can take much more time.
To ensure the highest possible performance, make sure that clocks are initialized to maximum before calling init function and also ensure that correct flash wait states are configured and that instruction cache is enabled:
https://www.nxp.com/docs/en/application-note/AN5191.pdf
Regards,
Lukas