Take the risk. It’s always worth it
Logical Perspective
If you stay in the current organisation with the current payscale, you are likely to get 15% increase, as you mentioned. And that too will take time from now. No motovation, no new tasks, no exposure
If you take chance to switch, you get better pay, a chance to reevaluate your interests, explore new things, work closely with Cofounders(which is a great learning). Worst case, if the company shuts, or XYZ situation happens, you can settle in 10-15% less pay. Stability is something I would not suggest you.