Section 17.5 of the
TALON SRX Software Reference Manual lists the throttle range as -1023 to +1023. A throttle of -19 is very, very small--less than 2%. You might need to increase the P value.
Note that the speed value is in encoder counts per 100 milliseconds. You will need to convert from RPM (or whatever speed units you use) based on the number of encoder counts per revolution. Note also that the encoder is always read in 4x mode, so a 250 cycle per revolution encoder is actually 1000 counts per revolution.