Yeah I'm scared of the process of dying too. If I just had a "die" button 100% that. Just be dead. In fact in an ironic way, fear of dying (how humans usually die in this day and age) is one of my main reasons to CTB. I'm terrified of getting old and degenerating and losing autonomy and dying slowly and agonisingly in a hospital bed.
SN also has an element of suffering to it and sometimes pain, albiet nothing excruciating unless I'm a rare outlier or something. The difference is it will only be for 15 minutes, not years of deterioration and old age pain, months of suffering, and days of agony. And it will be under my control.
But since prolonged suffering is one of my biggest fears, I'm still quite scared of those 15 minutes for SN as it is essentially still suffering, just the kinder and quicker of the two choices.
Feels like life has to get bad enough again for me to properly go through it without too much SI.