avoiding blunders on 2150 fide level

In the last 3 tournaments I threw away 3 games against significantly weaker oponents from equal or even better positions due to unneccessary blunders. Once I even took 15 minutes to make the losing move.

This really holds me back as I am losing a lot of rating points and don´t get paired against stronger opponents anymore. 

I am already doing a lot of tactical exercises (2200 on chesstempo, though not improving), but it doesn´t seem to help

I am rated about 2150 fide

Any advice?

Good rule of thumb is to take advice from people rated way below you with a grain of salt. I see all sorts of terrible advice given (with good intentions!) by people perpetually stuck with novice ratings.