sub 15 globaly

Did anybody experience that too? I sometimes (at least one a day) get just sub 15 or 15/16s. I have that for like 10-30 solves and have ao5s wich are sub 15 and even ao12s. That are mostly normal, fullstep solves. Not just the ones, in wich I particulary know the oll( still learning, i know like...