https://autowise.com/new-cars-under-15000/
Just buy them a new car if you want to spend 15k. No maintenance to worry about while they are in college. The cars will have the newest safety features as required by the DOT and be S L O W which is what you want for their safety.
They want something fast, fun, flashy, etc? They should buy it themselves with their money so they will appreciate it. You appreciate something a lot more if you worked for it vs. it being handed to you on a silver platter.