The most important question is current side effects? To advise properly, I'd need start weight, age, height, and loss timeline. But with no side effects, there's no reason not to increase the dose. Losing that much weight is a long-term health risk, and higher doses prevent obesity-related problems and maintain weight loss. That way you prevent diabetes, high blood pressure, high cholesterol, strokes, heart attacks, etc.
Also, how comfortable is your calorie intake? Are you always hungry? GLPs fix that. If you're still restricting, up the dose.
Two weeks of no change means nothing; fluid balance can fluctuate. If your diet hasn't changed and you previously lost weight, it's likely fluid.
If weight loss has slowed over time, it's a genuine stall. You're lucky to have lost so much and still have room to increase doses. It's common to stall at max doses before reaching the target. I don't think switching to Reta is crucial. You're responding well to tirz and probably have minimal side effects. Switching will disrupt your diet and increase side effects. Tirz will likely get you to your target at higher doses, so I see no advantage in swapping.