What are the differences between the MiG-15 and MiG-17?
I'm surprised no-one's mentioned the length - the MiG-15 has a much stubbier appearance than the MiG-17, because it was rather shorter (10.10m vs 11.26m)

The wings of the MiG-17 are angled at 45°, rather more than the MiG-15 (helpful to identify from above), and the tailplane is has a small amount of extra rake too.

Overall, the MiG-17 has a longer, sleeker profile than its older cousin. Here's a comparison, 15 in blue, 17 in red.