thank you for the answers! i think this will help to improve my game.

i'll try to ...
... play less hands
... play even lesser hands from ep (only pp's and ak/aq)
... (re)raise more often with good hands
... call raises less often
... attack the blinds more often
... make more c-bets
... play the river less aggressively

ok. i think i'm ready for the next 15k hands