He said it had “decent” interior. Tells me it needs work.
No mention of a recent paint job. Likely not great.
Add in reliability mods, sounds like $ invested just went north of $25 K.
We need pics and details.
For $15 K, it better be real nice and not need much. That said, an all stock 90,000 mi car will need plenty of $ thrown at it to be reliable.
There are completely done cars with the appropriate mods that aren't selling in that price range.