Go to yachtworld.com, enter Islander 36, and see what prices come up. Of the two boats you've mentioned, if they were both in good condition, the Islander is a better boat, but you've got to find (and pay for) better examples. 15k for a 36' boat will not cover the work you will need to do. If you're budget is 15k, find a smaller boat for 10-12k, and use the rest to fix/upgrade/etc.... Don't be in a rush, and look at this:
Boat Inspection Trip Tips
You've got a lot of reading and research to do so you have a better idea of what's even worth looking at. An Islander 36 at 9.5k screams "project boat" if not something for the sawzall and dumpster. One for 30k might be worth a look, but that's twice your budget. Both of the boats you posted are well within the 'run, don't look back' category given your descriptions.