as you car has driven ~150k and engine condition is also good as you said. So now its time to move little thicker oil than what you are using presently.
If you are still using 5/30, then its no recommended to use it more.
Secondly, caltex, shell, toyota, honda, pso, total, etc are the old names in the market and people are moving to synthetic n semi synthetic oils. Quality wise these local oils are not very good as compare with imported oils (subject they are not being repacked here).
I will strongly suggest you to use
ZIC M 15/40
change it after 3500~4000K
keep it using till your car completes 170k
after that simply shift to 20/50
but again, plz prefer imported companys and dont trust the quality of local oils any more.
Cheers with good luck.
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