indeed you shouldn't.
When i had Junoon, i was also bit annoyed by this loose tappet sound. (you may check my Junoon thread)
And i got my tappets over-tightened from a road side mechanic just to stop the sound and that idiot did it. 
And after that when i went to DYL center for tuning, the mechanic told me that tappets are over-tightened and could damage the engine in long run.
So then i learned the lesson that you shouldn't judge the tappets by sound only. Just let the mechanic adjust them according to the manual. Don't ask him to tighten them because you are feeling khur khur. If they are doing khur khur at well adjusted settings then let them.
By the way, for GS150 they don't even bother to check tappets before 5000Km. At 5000km they will check and adjust "If required". It's not CG125.
Also another factor could be engine oil here. May be it's the Kixx which is causing loud tappet sound.
Put whatever oil you were using before and i hope tappet sound would be same as before.
