When the engine of 150k car actually opens, it will be a nightmare and eat 30-40k expenses due to lack of care from previous owner, so better to run as it is, or go for full overhaul.
You will be wasting 10k on piston ring or valve work, as it a well known trap of mechanics. 6-7k estimate de kar baad mein 20-30k ka kharcha keh dety hain.