Hi there! I understand you're experiencing lag issues with SuperStar SMTOWN on your iPhone 6s Plus. That model is a few years old now, so some performance hiccups can happen with newer games. Let's see if we can improve the situation for you.

Could you tell me a bit more?
- When does the lag mostly happen? For example, immediately on startup, during specific gameplay moments, or after playing for some time?
- Have you tried closing other background apps or restarting your phone before playing?
- Are you connected over Wi-Fi or cellular data when playing?

Meanwhile, I can share some tailored tips for the iPhone 6s Plus and iOS 15.8.4 to help reduce lag in games:

1. Close Background Apps: Double-tap the Home button and swipe up apps running in the background to free up memory.
2. Reduce Visual Effects: Go to Settings > Accessibility > Display & Text Size and enable Reduce Transparency. This lowers the graphical load on your phone and can smooth performance.
3. Restart Your iPhone: Power off and back on to clear temporary cache and refresh system resources.
4. Check for Updates: Make sure both iOS and SuperStar SMTOWN are up to date; developers often improve performance in updates.
5. Lower Graphics Settings: If the game offers graphic settings, try reducing them to lower quality or frame rate options.
6. Free Storage Space: Ensure your iPhone has some free storage because low space can affect performance.

The lag often becomes more noticeable after a few minutes of gameplay due to the device heating up and the CPU throttling to prevent overheating, especially in the iPhone 6s Plus model2.

Try these steps and let me know if the lag improves or if it continues, so I can help you further. Does this sound doable?