Updates

These are the iOS options based on iPhone Model --> You need to Identify your iPhone model - Apple Support

• iOS 15 —> 6S / 6S Plus, SE (1st Gen and 2nd Gen), 7 / 7 Plus, 8 / 8 Plus, X, XR, XS /XS Max, 11,11 Pro /11 Pro Max, iPhone 12, 12 Mini, 12 Pro, 12 Pro max, iPhone 13, 13 Mini, 13 Pro, 13 Pro Max
• iOS 12.5.4 —> Final release supported on iPhone 5S, iPhone 6/6 Plus, 

Learn how to--> Update your iPhone, iPad, or iPod touch - Apple Support

sorry only the following models can get updates now

iOS 15 is compatible with these devices.

• iPhone 13
• iPhone 13 mini
• iPhone 13 Pro
• iPhone 13 Pro Max
• iPhone 12
• iPhone 12 mini
• iPhone 12 Pro
• iPhone 12 Pro Max
• iPhone 11
• iPhone 11 Pro
• iPhone 11 Pro Max
• iPhone Xs
• iPhone Xs Max
• iPhone Xr
• iPhone X
• iPhone 8
• iPhone 8 Plus
• iPhone 7
• iPhone 7 Plus
• iPhone 6s
• iPhone 6s Plus
• iPhone SE (1st generation)
• iPhone SE (2nd generation)
• iPod touch (7th generation)