I use 80pg/20VG (or less VG) so my cartos will work well longer.
Nicotine is TH and irritation, and is enhanced by heat like from the LR cartos and attys the 400mah+ batteries can use
PG is thin, lets through the most flavor, the most of nicotine's TH and irritation, makes thin visible vapor
VG is thick, dulls/smooths everything PG lets through, makes thicker more persistent vapor
If the nicotine level is too harsh for you, try a lower nicotine level. You won't have a nic fit - you'll have an easier time taking good sized drags and you can always do an extra drag to make up the difference. If you continue to vape a nicotine and PG/VG and heat combination that is too irritating for you then your mouth, throat, sinuses and even lungs can get irritated.