check the usual under chassis for corrosion mate - pay attention to the rear subframe but to be honest if its not been here long that shouldnt be a problem.
look for oil leaks particularly under the turbo area (coolant leaks here also) and on the front timing case. all the usual oil, smoky exhaust, rust, brake pads checks apply - look for badly/unevenly worn tyres, door, bonnet, boot shuts line up.....
look for signs that its been meddled with and put back to standard ie. screw holes in the dash, non standard looking hoses in the engine bay and whatnot. check the box is not noisy and works well same as the rear diff (can make a little noise but shouldnt be bad) and check clutch doesnt slip. gear changes should be smooth, but can be a little notchy when moving off from cold.
listen for knocking suspension, make sure it doesnt pull to one side when driving.......
mainly see that it drives well. if its sat ticking over when you get there ask why.....could be trying to hide something. if standard turbo should come in smoothly and progressively with no smoke from the exhaust - shouldnt really kick you. keep an eye on the temp gauges and warnings (make sure they all work with ignition on)
listen for vvt rattle (a top end rattle that is there when cold is common and not necesarily a deal breaker, but if its there all the time it could be an expensive problem)
bear in mind its very rare to find an s15 that hasnt had some form of repair done so dont let a well repaired car put you off or you may be looking forever......but if its been repaired badly or extensively id walk
thats my bit, think ive covered most things, there arent many s15 specific things - apart from the drive and checking the engine over most things are pretty generic checks you' make anyway - im bound to of forgot something and there are far more knowledgable people than me on here so hang about for some more replies:thumbs:
good luck!