In this paper, a transmission line circuit model of a magnetically insulated transmission line(MITL) system has been developed for a 15 MA Z-pinch driver (CZ-15). The current loss characteristics of multi-level MITLs and the ion emission due to expansion of anode and cathode plasma during the PHC and inner-MITL region are analyzed. The temporal and spatial distribution of current loss of outer-MITL and ion current of the PHC and inner-MITL of the CZ-15 driver are obtained. Results show that the first electron emission happens at the end of constant-impedance MITL and the beginning of constant-gap MITL, and the end of constant-gap MITL firstly achieve fully magnetic insulation. Electron emission at the start of load current and the duration is about 25 ns, which is short for a single pulse and has little effect on the rising edge and peak value of the load current. The waveform of the electron flow functioning as time resembles a saddle shape, whose amplitude goes up first, then it goes down, and then increase again. The electron flow current decreases from upstream to downstream in constant-gap MITL in space. The starting time of the loss current of the PHC is synchronized with the gap closing time. The loss current amplitude increases rapidly, reaching 4 MA at the peak load current time and 6.5 MA in the end. During the inner-MITL region, the main positive ion species are protons and Oxygen 2%2B. At the beginning, the ion loss current of proton is larger than that of Oxygen 2%2B, and then the protons are quickly magnetically insulated due to the small charge-to-mass ratio. The ion loss current of the inner-MITL region mainly increase after the peak load current time, and its peak value is 2.1 MA. Given the input conditions, the stack is going to deliver current about 18 MA and hold voltage about 2.3 MV, the peak load current is about 13.5 MA.