The standard iPhone 15 uses stretch-release battery adhesive and needs fresh back-glass adhesive after opening. Apple also documents separate display and USB-C connector repairs.
What to check before buying
iFixit score
7/10 · Rubric v1.6. Source: Smartphone repairability scores (iFixit). How to read the score.
Battery and enclosure
iFixit’s battery guide shows stretch-release strips under the standard iPhone 15 battery. Reassembly calls for new back-glass adhesive. The 15 Plus and Pro use different parts and procedures.
Display and charging parts
Apple’s manual covers the display, back glass, USB-C connector and cameras separately. Some component replacements also call for Repair Assistant or System Configuration after assembly. A used phone with a previous back-glass repair should have flush edges and a working USB-C port.