Is the base iPhone 15 waterproof/resistant

No iPhone is waterproof.

Even the water resistance ratings are the result of controlled laboratory tests. Not from exposing a phone to the sorts of things it might encounter on kayaking trips.

Don’t intentionally get it wet.

Keep it in a waterproof container.

Water damage is almost always “terminal” and is NEVER covered under an Apple warranty.

If you must take pics, purchase an appropriately waterproof camera.

When new and undamaged, and when tested with pure water under laboratory conditions, an iPhone 15 will probably survive a very shallow dunking.

Probably.

In reality, use a dry bag for your phone, and for anything else dunk-sensitive.

Like their phones, the contents of many folks’ wallets don’t do so well when dunked, either.

About splash, water, and dust resistance of iPhone 7 and later - Apple Support

To prevent liquid damage, avoid:

• Swimming or bathing with your iPhone
• Exposing your iPhone to pressurized water or high velocity water, such as when showering, water skiing, wake boarding, surfing, jet skiing, and so on
• Using your iPhone in a sauna or steam room
• Intentionally submerging your iPhone in water
• Operating your iPhone outside the suggested temperature ranges or in extremely humid conditions
• Dropping your iPhone or subjecting it to other impacts
• Disassembling your iPhone, including removing screws

Minimize exposing your iPhone to soap, detergent, acids or acidic foods, and any liquids — for example, perfume, insect repellent, lotions, sunscreen, oil, adhesive remover, hair dye, and solvents. If your iPhone comes into contact with any of these substances, follow the instructions to clean your iPhone.