Regarding SPF, is anything over 15 "a waste"?

Sun Protection Factor (SPF) is an indication of how much a product can protect the skin from sunburn (UVB rays.). When applied appropriately, SPF 15 sunscreens block 93% of the suns UVB rays, where SPF 30 sunscreens block 97% of the UVB rays. Beyond SPF 50, which provides about 98% protection from UVB rays, the increase in ultraviolet protection is negligible. Because there is insufficient data to show that products with SPF values higher than 50 provide greater protection for users, the FDA has proposed a cap of SPF 50. To date, the FDA is still reviewing this issue.

SPF ratings do not give any indication of how well a product protects against UVA rays (those that cause skin aging and skin cancer.) The American Academy of Dermatology recommends that broad spectrum (protects the skin from both UVA and UVB rays) sunscreens of SPF 30 or higher be used.

Refer to Sun Facts for more information.