Thread: Dirty or Clean barrel?

Hi there... ok, don't get me wrong, I keep a very clean rifle(s), however just having bought a tikka varmint 223, I find it shoots clean at 1.5inchs at 100m, and after 15 or so shots it tightens up to .3 to. 5 moa.
So my question to the team is, should I leave this rifle semi dirty or fouled( after the 15 or so rounds through it) to have the best accuracy the next time I make a shot with it?
Apologies if this has been covered off elsewhere, I couldn't find any link.