all depends on the price and how much work you are prepared to potentially put in for the exact car you want.
I personally would stay away from a JTS at any mileage but thats another debate, they are capable of high miles with the right owner if its got to 150k it can't have been treated badly at all, I would suspect at that age it will be on its 3rd clutch,set of wishbones and probably a second rad.
as Scotty has said check all of the usual suspects and you should be fine, JTS specific problems are camshaft wear,coil packs and Lambda's normally the exhaust side cams, won't go into the reasons why here, but I owned one in a GT. It's well worth you doing some research on the JTS before you pull the trigger, I wish I had..a little more knowledge could have saved me £1500
I see you are in Ireland, I have a mate there so know people consider 150k differently to the UK, VRT tax makes it expensive to import anything without paying a huge premium so there is less choice, especially with a niche marque like Alfa.
all things considered go for it but just make sure there are no terminal bodywork issues. give that underside a thorough inspection
and on any car at 150k be prepared to throw the engine in the bin and start again at some point if of course the rest is sound, a good JTS can be had for around £250 on ebay.
best of luck!