Time per move

"the average game takes 30-40 moves" ++ Yes, most games are essentially decided by move 30.
"If playing on a 10 minute clock"
++ 10 minutes * 60 seconds/minute / 30 moves = 20 seconds / move
"Should you really be paying that much attention to the clock? "
++ No you should not look at the clock, only at the board. Always play the same time control so go develop a feeling for the right pace.
"Sometimes I find it hard to do the mental blunder check and find the right move in that 15 seconds" ++ Play 15|10 then you have 40 seconds per move.