How to simulate a simplified model of crosstalk effect in LTspice?
consider this. 

By the way, as the analog-mux switches from one source to another source, the new source MUST provide charge to erase the voltage
of the previous source.







simulate this circuit &ndash; Schematic created using CircuitLab

by the way, I ignored ON_resistance of the FETs. Also ignored inductance of the IC package, of bondwires, of PCBtraces, of VDD bypass caps for the Multiplexor power (+5, +15, -15)

Sampling rate will not affect the crosstalk, unless your rate is so fast that the LOGIC gates that drive the analog-switches are not able to fully control the analog-switches state to fully on or to fully off. This likely will occur at some multiplexing rate well above 1MHz. Also depends on how clean YOU maintain the GND and the VDD of the IC; will you simulate that?
Place 10nanoHenry in each VDD connection. 

Search around; I already provided a fully-detailed schematic for this type of question, months ago.