5% CTR is okie but as many have already told you get rid of the images next to the ads as these does imrove the click thru rate but its against the TOS
CTR of 5% is good, but 10% would be perfect Btw, paul, your blog is quite traffic untargeted, as so are your ads, that is the reason for your low CTR...
Just remove the images it is against to google tos. I think clickable rate depends on niche you selected.
5% CTR is really acceptable. Your CTR should not exceed 15% daily, then only Google suspects you. (Up to 10 % is acceptable). CTR is solely depends on the niche you've chosen.
Where did you learn that google suspects you if it goes above 15%? Most days here I run 30-60% and no problems =\