Just had a look at the code and the choice is in Episode 8. You have to pull out of the simulation and clear it. The events with Eva in Episode 15 are triggered when you haven't cleared the sim in Episode 8 and went inside a sim with Eva in Episode 13. There are other choices regarding the simulation in Episode 15 (during Eva's coma). The variables for this trigger are ep013_douvis_simulation and ep008_simulation_clear. If you bring up the developer console inside the game (Shift + O) and type either of those variables, they should show up as True if you went into the sim in Episode 13 and didn't clear it in Episode 8. Hope that clarifies it somewhat.