chore: [SDK-5034] bump iOS minimum deployment target from 11 to 15

[fadi-george]

Description

One Line Summary

Raise the iOS SDK minimum deployment target from iOS 11 to iOS 15.

Details

Motivation

Docs and App Store metadata already describe a higher minimum than the code (iOS 11). Current App Store submissions with Xcode 26 only support a deployment range starting at iOS 15. Bumping directly to 15 aligns the SDK with that toolchain baseline in one breaking change instead of stepping through 12 first.

Scope

• CocoaPods podspecs, Xcode project deployment targets (including leftover 9.0 SDK/test targets and the DevApp App Clip at 14.0), and Package.swift platforms: [.iOS(.v15)]
• README and GitHub bug-report template
• Unwrap obsolete @available(iOS 11) guards in IAM UI
• Does not rebuild vendored XCFrameworks (that happens on the next release)
• Does not change the historical v5.0.0 MIGRATION_GUIDE.md
• Does not bump the KMP submodule podspec (still 11.0)

Testing

Unit testing

No new tests. This is a deployment-target / availability cleanup.

Manual testing

• xcodebuild -list on OneSignal.xcodeproj succeeds
• OneSignalCore built for iOS Simulator; compiler used -target ...-ios15.0
• Full UnitTestApp CI depends on a fresh KMP XCFramework build (same as existing CI)

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
• I have reviewed this PR myself, ensuring it meets each checklist item

Made with Cursor

[abdulraqeeb33]

If we could figure out what min OS version does Apple accept, that would be so helpful

[fadi-george]

If we could figure out what min OS version does Apple accept, that would be so helpful

I think is 15 as other sdks like Airship and Firebase also do 15+ (16+ for airship)